General Description Maxim's family of line drivers/receivers are intended for all RS-232 and V.28/V.24 communications inter- faces, and in particular, for those applications where +12V is not available. The MAX230, MAX236, MAX240 and MAX241 are particularly useful in battery powered systems since their low power shutdown mode reduces power dissipation to less than 5uW. The MAX233 and MAX235 use no external components and are recommended for applications where printed circuit board space is critical. All members of the family except the MAX231 and MAX239 need only a single +5V supply for operation. The RS-232 drivers/receivers have on-board charge pump voltage converters which convert the +5V input power to the +10V needed to generate the RS-232 output levels. The MAX231 and MAX239, designed to operate from +5V and +12V, contain a +12V to -12V charge pump voltage converter. Since nearly all RS-232 applications need both line drivers and receivers, the family includes both receiv- ers and drivers in one package. The wide variety of RS-232 applications require differing numbers of drivers and receivers. Maxim offers a wide selection of RS-232 driver/receiver combinations in order to minimize the package count (see table below). Both the receivers and the line drivers (transmitters) meet all EIA RS-232C and CCITT V.28 specifications. MAAL/VI +5V Powered RS-232 Drivers/Receivers Features @ Operates from Single 5V Power Supply (+5V and +12V MAX231 and MAX239) @ Meets All RS-232C and V.28 Specifications @ Multiple Drivers and Receivers @ Onboard DC-DC Converters @ +9V Output Swing with +5V Supply @ Low Power Shutdown <1yA (typ) @ 3-State TTL/CMOS Receiver Outputs @ +30V Receiver Input Levels Applications Computers Peripherals Modems Printers Instruments Selection Table No. of No. of Neer Power Supply Voltage RS-232_RS-232 Components Low ae No. of Pins Drivers Receivers MAX230 +5V 5 0 4 capacitors Yes/No 20 MAX231 +5V and +7.5V to 13.2V 2 2 2 capacitors No/No 14 MAX232 +5V 2 2 4 capacitors No/No 16 MAX233 +5V 2 2 None No/No 20 MAX234 +5V 4 0 4 capacitors No/No 16 MAX235 +5V 5 5 None Yes/Yes 24 MAX236 +5V 4 3 4 capacitors Yes/Yes 24 MAX237 +5V 5 3 4 capacitors No/No 24 MAX238 +5V 4 4 4 capacitors No/No 24 MAX239 +5V and +75V to 13.2V 3 5 2 capacitors No/Yes 24 MAX240 +5V 5 5 4 capacitors Yes/Yes 44 (Flatpak) MAX241 +5V 4 5 4 capacitors Yes/Yes 28 (Small Outline) Patent Pending MAXI Maxim Integrated Products 3-1 MAXIM IS a registered trademark of Maxim Integrated Products bb o-OECXVNMAX230-241* +5V Powered RS-232 Drivers/Receivers ABSOLUTE MAXIMUM RATINGS seen eee e tenes -0.9V to +6V Short Circuit Duration (Vee - 0.3V) to +14V TOUT cece eee e eee entree tect tte ents continuous rene nee nee n nee nee nee +0.3V to -14V Power Dissipation CERDIP 2.0... ccc cece cece ec eee net eee es 675mW -0.3 to (Vee + 0.3V) (derate 9.5mW/C above +70C) ceed ee eee ene ene ne ened beeen eee eee +30V Plastic DIP 2... i. cece eee eee eet eee G7SIMW (derate 7MW/C above +70C) a ran (V* + 0.3V) to (V> - 0.3V) Small Outline (SO) 2.0... 0. ccc eee cece eee ee 375mW Rout cece cree e teen e teen n nena es -0.3V 10 (Vee + 0.3V) (derate 7MW/C above +70C) Lead Temperature (soldering 10 seconds) ........... +300 C Storage Temperature -65C to +160C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation ai the device at these or any other conditions above those indicated tn the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (MAX232, 234, 236, 237, 238, 240, 241 Vog = 5V + 10%; MAX233, 235 Voge = 5V + 5%; MAX231, 239 Veco = 5V + 10%, V* = 7.5V to 13.2V; T, = Operating Temperature Range, Figures 3-14, unless otherwise noted.) PARAMETER CONDITIONS MIN. TYP. MAX. UNITS Output Voltage Swing tn See guts loaded +5 +9 v Voc Power Supply Current No load, Ta = *25C 5 10 mA MAX231, MAX239 0.4 1 V" Power Supply Current MAXoaT and MAX239 only aoe = = ma Shutdown Supply Current Figure 1, Ta = +25C 1 10 BA input Logic Threshold Low Tin EN, Shutdown 0.8 v Input Logic Threshold High Tw 20 v EN, Shutdown 2.4 Logic Pullup Current Tin = OV 15 200 uA RS-232 Input Voltage Operating Range -30 +30 Vv RS-232 Input Threshold Low Voc = SV, Ta = +25C (MAX231, 239 V" = OV) 0.8 12 v RS-232 Input Threshold High Voc = SV, Ta = +25C (MAX231, 239 V* = 12V 17 2.4 v RS-232 Input Hysteresis Veco = SV Q2 0.5 1.0 v RS-232 Input Resistance Ta = +25C, Voc = 5V 3 5 7 kQ TTL/CMOS Output Voltage Low loyr = 1.6mA (MAX231-233, loyr = 3.2MA) 0.4 Vv TTL/CMOS Output Voltage High lout = -1.0mMA 3.5 v TTL/CMOS Output Leakage Current EN = Veo, OV <= Royt <= Veo 0.05 +10 HA Output Enable Time (Figure 2) MAX235, MAX236, MAX239, MAX240, 241 400 as Output Disable Time (Figure 2) MAX235, MAX236, MAX239, MAX240, 241 250 ns Propagation Delay RS-232 to TTL 05 us Instantaneous Slew Rate - eC Nowe) 30 V/us R, = 3kQ, C, = 2500pF Transition Region Slew Rate Measured from +3V to -3V 3 Wus or -3V to +3V Output Resistance Veo = V7 = Vo = OV, Vout = 2V 300 | a RS-232 Output Short Circuit Current +10 mA Note 1; Sample tested. 9-2 MAXIM+5V Powered RS-232 Drivers/Receivers Typical Operating Characteristics TRANSMITTER SLEW RATE MAX239 TRANSMITTER OUTPUT VOLTAGE TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE vs. V+ VOLTAGE S. Voc VOLTAGE 5 12 9 Veo = 5 Ay = KO/OUTPUT 1 | ig = 3OQ/OUTPUT = iq. | 27H? CAARGE PUMP caPHCrTORS 3 a # 9 Val = = a s | 2 2, Z #2 z 3 4 = 5 Von, 1 TO 5 TRANSMITTERS z LOADED = | 5 5 4 4 4 0 = 50D 500 0002800 5 6 7 8 9 WH B 45 875 5.0 5.25 55 LOAD CAPACITANCE (pF) ve Ver M V* SUPPLY VOLTAGE V- SUPPLY VOLTAGE CHARGE PUMP OUTPUT IMPEDANCE vs. LOAD CURRENT vs. LOAD CURRENT VS. Voc (MAX230, 234-238, 240, 241) (MAX230, 234-238, 240, 241) (MAX230, 234-238, 240, 241) ALL CAPS 47,F ALL CAPS ATF eur + Rou u Ul = pe . = 0 10 SLOPE = Rout -10 2 Ss a 3 = oo Pour = Ioan INCLUDES 5 ee = 4 4 TRAASANTTER OUTPUT = > CURRENTS 3 . 7 a _ Rour- = 6 4 2 huoag INCLUDES 3 (0 5 | TRANSMITTER OUTPUT 4 4 Lousaints 4 b 0 5 0 6 OB B MO B 0 5S -ID -1 2-25-85 4 a5 5 55 6 V7 QUTPUT GUARENT [mAl Vo OUTPUT CURRENT (mal Voc M1 ov 'suuroown + V | EN sco Vee a INPUT = Fr _| | QUTPUT ENABLE TIME + 35v =| AECEIVER Dev OUTPUT C, = 150 pF + ay EM INPUT gy >| ton Vou - QV RECEIVER y 5v OUTPUTS o RL = then 2 Vou + O.1 Figure 1. Shutdown Current Test Circuit MAAI/VI Figure 2. Receiver Output Enable and Disable Timing sb PS-OECXVN+5V Powered RS-232 Drivers/Receivers *5 INPUT wc 16 Lead Smal! Outline Figure 4, MAX231 Typical Operating Circurt 9-4 * + a WyF 8 av 41yF +5 70 +10V &% ov VOLTAGE DOUBLER N 47uF +10 TO -10V >< 1 VOUIASE INVERTER souk a! a bv = Tw Tlout MAXIM MAX230 Tau T2out TTL/CMOs iweuts] 73" Tout | as.z32 QUTPUTS Tan Tour 20 Lead Small Outline TSH TSqut also available. SHUTDOWN Figure 3. MAX230 Typical Operating Circuit +5V INPUT +75V TD -12V VS ct a) y* c- 13) Vee VO anaxin Fl eNO AngE 2 We Tor CE maxesr = FD Tour iw C2. +12 TO -12 2. [E HD RI VOLTAGE CONVERTER 3 IN tN v- 7 cz R2Zyy7 8) Blogz Alpe 12, Thy +5V LE wy amas ~ 14 Lead Plastic DIP alt > Tour fit + /CMOS AS-232 ve TNPUTs a. 3 OUTPUTS Vee 7] T [> Tour 4 MAXtm GND MAX231 Tour Rly QE Rlour at Alfio al nN Truscmas | A8-232 N OUTPUTS INPUTS MAKI+5V Powered RS-232 Drivers/Receivers +5V INPUT = i inet > 1OuF > oa <r 4 . 6 LS) 1 cy" Vee eae #5 TO *10V we 63V tT cl-__VOLTASE DOUBLER *tov 8 . " . a +E ee +10V 10 -10V 10v wee Slop VOLTAGE INVERTER a OF by MAXIM >5Y + iv A MAX232 = wa, ann within ; tl Tout 14 * " AS-232 " . TgPUTs 400k. GUTPUTS 10g T2in T2out 7 120 Bl out Al Alinta 16 Lead Small Outline rruemos gee aszae also available. GUTPUTS i. INPUTS gp A2our = RaW ew (4 gee Guo = 15 Figure 5. MAX232 Typical Operating Circurt = +5V INPUT AS-2320 wu myc nots T2 WO 20) 2 OUT TiN [2] iS} R2 IN RI oUT LB] 8] T2 OUT RI IN [4] fiz] V- MAXIM _ TTL/CMOS RS-2326 TI OUT 5] MAX233 i6) C2 OUTPUTS INPUTS GND a 15) C2+ Veo LZ fia] y+ ow e a 1. rm - DO NOT MAKE ono (8 iz] v CONNECTION i c2- [id] Ti] C2+ THESE PINS INTERNAL oe . : 8 Small Outline Not Available INTERNAL +10V POWER SUPPLY Figure 6. MAX233 Typical Operating Circuit MAAIWI 9-5+5V Powered . RS-232 Drivers/Receivers * | +5V INPUT a 6 L l0uF So irae ln : Te Gav atur +5 TO +10V ve n bay TS fa VOLTAGE DOUBLER C+ 4TuF _|* *10V TO -10V y- 2 lev Fu VOLTAGE INVERTER >< ce tue <q +5v 7 lev MAXIM = MAX234 400k) 4] tlw [> Tout ft Ro +y 400k0. 3 3] Tn + 2 Teaut $2 TTL/CMOS RS-232 INPUTS 400K OUTPUTS 13] T3w T3out | 16 . 13 . i 16 Lead Small Outline 400k also available. 14] Tay [> T4our | 15 ena i Figure 7, MAX234 Typical Operating Circuit = +5 INPUT Voc Tin Tout T~Y Tain T2gut T4yur 1] 24) A3y T3gyr [2] [23] R3pyt mewn Tan Tagur 7 S23 Tow @] 22] T5ry T2oyr 2] SHUTDOWN Tw Taaut Rw EL Anaxian [5 EN R2qyr CE] MAX235 FS] T5qy7 15m Teout Tay EZ] 18} Ray Mout AW Ty & 7) RApyr R 9 6 Nour 2 76) T4iy Root 2m Alyy [0] 5] T3y GND [1] [14] REgyr MOS | RSour Wm | AS2SE Voc [2] 3) RSiy Rgut Raw 0.600" Wide Package Only Small Outline Not Available ASour AS EN SHUTDOWN Figure 8. MAX235 Typical Operating Circuit 9-6 MAKIM+5V Powered RS-232 Drivers/Receivers +SV INPUT . 2 i oe ND rear] Fa Thur a wi we as 3 Tour 4 23) R2y i T2qut BI [22] R2qut Tout N Rly 4 21] SHUTDOWN aA Rl ur CE MAA [20] EN Teout TTL/CMOS AS-232 T2y fe] MAX236 *9) Tay nears QUTPUTS Thy 18] T3iy T3aut GND (&] 77] Rgut Voc iF] 6) R3y T4out Ci+ fo] 5] y~ Vo 4] C2- Alm ci- 73] C2+ TTL/GMOS RS-232 OUTPUTS Ram F inPUTs 24 Lead Small Outline fn also available. SHUTDOWN Figure 9. MAX236 Typical Operating Circuit *5V INPUT Our aay a wn C2 wn. Tout 24] T4gyt w co. wunwe ven OuF Toyr 2 [23] R2iy te T2out By [22] R2our Th Tlout Alyy [24 [21] TSiy Mout EY wraxian F2 Tour TZ Teout 6 7 19 Tay [E] maxza7 [81 Thy Troms!) 15, Tagur | 88-292 Ty ZZ 18} T3yy INPUTS OUTPUTS GNO (2 7 R3qut tis sour Ci+ Le] 8) y- T5in TSour v* fy 14) C2- ci- [2] 3) C2+ lout alm TTL/CMOS RS-232 urpurs) *20uT R2m Tt NPUTS 24 Lead Small Outline also available. Rout i) Figure 10. MAX237 Typical Operating Circuit MAAIL/VI 9-7MAX230-241* +5V Powered RS-232 Drivers/Receivers +6 INPUT eer 4iuF cle +64 TO -10 yr . aay Cle vocTase pauaLer T2oyr (24) T3qyr a c2- voutase wearin VT tut Tloy C2] 23] Rain w * a Ry Rout Tw Thowt R2gur C4] 21] T4yy Thy Ey axial Tour riLemos Tam TEU | og on RAlouy = MAX238 [13] T3y INPUTS OUTPUTS Riy 18] T2in TS T3aut eno [21 Rgur T T Veo 7) dy " on ci+ Le] fs] y- Rlout Rin vo [14] C2- ci- Ee] 73) C2+ Rau Ran TTL/CMOS AS-232 DUTPUTS INPUTS . A3qut Rain 24 Lead Small Outline also available. Aleut hw Figure 11. MAX238 Typical Operating Circust 75V-1220 +SVINPUT INPUT . Vcc a? uF c +10 TD -10y Nn C VOLTAME INVERTER: 1DuF Moy G * Aly 2 6ND [a Tin Tiput Veo C4 TTLCMGS aa202 ve inputs) 2" Teovt | gureurs c+ [8] T3in T3qut c- v--[7] Rlour Blin AS, ASqyy Gia] an R 1 TTL/CMOS AS-232 _ a outputs | Rieu "ow | wputs Rqut Rain * NC - No Connection : Rs 24 Lead Small Outline Raut also available. _ EN nee Figure 12. MAX239 Typical Operating Circuit 9-8 MAXI+5V Powered RS-232 Drivers/Receivers +5V INPUT (uF ow alr w we VOUTAae VERE w Th Tlout T2a T2out TTL/EMOS | 13, Tagyr | 88-282 MAXIM ; INPUTS NTF guTPUTs MAX240 Ta Tour TSn TSout Rlourt Rlix R2qut Ry TTL/CMOS RS-232 4d Lead P Flatoak Onl aurpurs | 4" F3m | INPUTS ead Plastic Flatpal n P y Rgut Mn RSqut Row aN SHUTDOWN Figure 13. MAX240 Typical Operating Circuit. +5V INPUT T3out ~ (28) TAgut 7 a 2. Ttout = [27] R3iN ay T2out 25} R3uT a vache VETER 1 R2In (a 125] SHUTDOWN aan a) R2outT Ey [24] EN Thy Tr Tlout T2 mn WO A axcian (2 PAIN Tem Tout TUN TZ] Maxa4y [22] Rout TTL/CMOs a RS 27 Rlout Ca 2a] Tay PUTS | Ta Tout Rin [1 [20] T3in = T4m Tut GND fio! [79] R5ouT Vec a iH} ROSIN Alout Riw Ci+ [2 17 YO a Pa R2gut R2w Vt fis] 16] C2- - TTL/cMas AS-232 Cl [4 15] C2+ ourpurs 7 P07 Fam | inputs Rqur Ray 28 Lead Wide Small Outline Onl y RSqut RSin Ey SHUTDOWN Figure 14. MAX241 Typical Operating Circuit MAXI 29 bP S-OECXVNMAX230-241* +5V Powered RS-232 Drivers/Receivers Typical Applications Figures 3 through 14 show typical applications. The capacitor values are non-critical. Reducing the capa- citors C1 and C2 to ipF will slightly increase the impedance of the charge pump, lowering the RS-232 driver output voltages by about 100mV. Lower values of C3 and C4 increase the ripple on the V and V outputs. If the power supply input to the device has a very fast rate-of-rise (as would occur if a PCB were to be plugged into a card cage with power already on), use the simple RC filter shown in Figure 15. This bypass network is not needed if the Vcc rate-of-rise is below 1Vius. All receivers and drivers are inverting. The ENable control of the MAX235, MAX236, MAX239, MAX240 and MAX241 enables the receiver TTL/CMOS outputs when it is at a low level, and places the TTL/CMOS outputs of the receivers into a high impedance state when it is a high level. When the Shutdown control of the MAX230, MAX235, MAX236, MAX240 and MAX241 is at a logic 1 the charge pump is turned off, the receiver outputs are put into the high impedance state, V" is pulled down to Vcc, Vis pulled up to ground, and the transmitter outputs are disabled. The supply current drops to less than 10pA. Detailed Description The following sections provide supplementary infor- mation for those designers with non-standard appli- cations and for those with interest in the internal operation of the devices. The devices consist of 3 sections: the transmitters, the receivers, and the charge pump DC-DC voltage converter. +SV to+10V Dual Charge Pump Voltage Converter All but the MAX231 and MAX239 convert +5V to +10V. This conversion is performed by two charge pump voltage converters. The first uses capacitor C1 to double the +5V to +10V, storing the +10V on the V7 output filter capacitor, C3. The second charge pump voltage converter uses capacitor C2 to invert the +10V to -10V, storing the -10V on the V output filter capa- citor, C4. The equivalent circuit of the charge pump section is shown in Figure 16. A small amount of power may be drawn from the +10V (V"} and -10V (V)} outputs to power external circuitry. The typical characteristics graphs show the typical output voltage vs. load current characteristics. 470 1OyF. B.3v Tm |e 3 (Our se Chypass 16 6.a T Vee = ve TOyF, 16 at LY ey. pop. ca MAXIM + 3y y= MAX232 lof ay op b+ lope Le iv 7 2 Ce- a Figure 15. Protection from High a Voc 90-70__- i GND. {-4 7 1 GND Q= L _I | a LE cf 3a Figure 16. Charge Pump Diagram. 9-10 MAXAIAIFor applications needing only the +5V to +10V charge pump voltage converter, the MAX680 is available. The capacitor values for C1 through C4 are non- critical. At the 15kHz typical switching frequency of the voltage converter, a 14uF capacitor has approxi- mately 109 impedance, and replacing the 4.7uF and 10uF capacitors shown in the typical applications with 1F for C1 and C2 will increase the output impedance of the V* output by about 10Q and the output impedance of V- by about 209. Lowering the value of C3 and C4 increases the ripple on the V* and V~- outputs. Where operation to the upper tem- perature limit is not required, or Veco will not go below 4.75V, C1 and C2 can be 1uF, and C3 and C4 can be 1y4F per output channel (1uF if one transmitter is used, 5uF if five transmitters are used). There are parasitic diodes which become forward biased if V* goes below Vcc or V_ goes above ground. When in the shutdown mode (MAX230, MAX235, MAX236, MAX240 and MAX241 only), V" is internally connected to Vcc by a 1kQ pulldown, and Vis internally connected to ground via a 1kQ pullup. The MAX233 and MAX235 contain all charge pump components, including the capacitors, and operate with NO external components. The MAX231 and MAX239 include only the V to V charge pump, and are intended for applications which have a +5V supply and either a +12V + 10% supply or a 75V to 13.2V battery voltage. When operating with V* greater than 8.0V, both capacitors can be 1pF. Driver (Transmitter) Section The transmitters or line drivers are inverting level translators which convert the CMOS or TTL input levels to RS-232 or V.28 voltage levels. With +5V Voc, the typical output voltage swing is +9V when loaded with the nominal 5kQ input resistance of an RS-232 receiver. The output swing is guaranteed to meet the RS-232/V.28 specification of +5V minimum output swing under the worst case conditions of all trans- mitters driving the 3kQ minimum allowable load impedance, Voc = 4.5V, and maximum operating ambient temperature. The open circuit output voltage swing is from (Vt - 0.6V) to V-. The input thresholds are both CMOS and TTL com- patible, with a logic threshold of about 25% of Vcc. The inputs of unused drivers sections can be left unconnected; an internal 400kQ input pullup resistor to Vcc will pull the inputs high, forcing the unused transmitter outputs low. The input pullup resistors source about 12uA, and the driver inputs should be driven high or open circuited to minimize power supply current in the shutdown mode. MAXAI/VI -+-5V Powered RS-232 Drivers/Receivers When in the low power shutdown mode, the driver outputs are turned off and their leakage current is less than 1A with the driver output pulled to ground. The driver output leakage remains less than 1A, even if the transmitter output is backdriven between OV and (Vcc + 6V). Below -0.5V the transmitter is diode clamped to ground with 1kQ series impedance. The transmitter is also zener clamped to approximately Voc + 6V, with a series impedance of 1kQ. As required by the RS232 and V.28, the slew rate is limited to less than 30V/us. This limits the maximum usable baud rate to 19,200 baud. Receiver Section All but the MAX230 and MAX234 contain RS-232/V.28 receivers. These receivers convert the +5V to +15V RS-232 signals to 5V TTL/CMOS outputs. Since the RS-232C/V.28 specifications define a voltage level greater than +3V as a Q, the receivers are inverting. Maxim has set the guaranteed input thresholds of the receivers to 0.8V minimum and 2.4V maximum, which are significantly tighter than the -3.0V minimum and +3.0V maximum required by the RS-232 and V.28 specifications. This allows the receivers to respond both to RS-232/V.28 levels and TTL level inputs. The receivers are protected against input overvoltage up to +30V. The 0.8V guaranteed lower threshold is important to ensure that the receivers will have a logic 1 output if the receiver is not being driven because the equip- ment containing the line driver is turned off or disconnected, or if the connecting cable has an open Circuit or short circuit. In other words, the receiver implements Type 1 interpretation of fault conditions (7 of V.28, 2.5 of RS-232C). While a OV or even a -3V receiver threshold would be acceptable for the data lines, these lower thresholds would not give proper indication on the control lines such as DTR and DSR. The receivers, on the other hand, have a full 0.8V noise margin for detecting the power-down or cable-disconnected states. The receivers have a hysteresis of approximately 0.5V, with a minimum guaranteed hysteresis of 200mV. This aids in obtaining clean output transitions, even with slow rise and fall time input signals with moderate amounts of noise and ringing. The propagation delays of the receivers are 350ns for negative-going input signals, and 650ns for positive-going input signals (see Typical Characteristics graphs). The MAX239 has a receiver 3-state control line, and the MAX235, MAX236, MAX240 and MAX241 have both a receiver 3-state control line and a low power shutdown control. The receiver TTL/CMOS outputs are in a high impedance 3-state mode whenever the 3-state ENable line is high, and are also high impe- dance whenever the Shutdown control line is high. 9-11 sb PC-OECXVNMAX230-241* +5V Powered RS-232 Drivers/Receivers Review of EIA Standard RS-232-C and CCITT Recommendations V.28 and V.24 The most common serial interface between electronic equipment is the RS232 interface. This serial inter- face has been found to be particularly useful for the interface between units made by different manufac- turers since the voltage levels are defined by the EIA Standard RS-232-C and CCITT Recommendation V.28. The RS-232 specification also contains signal circuit definitions and connector pin assignments, while CCITT circuit definitions are contained in a separate document, Recommendation V.24. Originally intended to interface modems to computers and terminals, these standards have many signals which are not used for computer-to-computer or computer-to-peri- pheral communication. Serial interfaces can be used with a variety of trans- mission formats. The most popular by far is the asynchronous format, generally at one of the standard baud rates of 300, 600, 1200, etc. The maximum recommended baud rate for RS-232 and V.28 is 20,000 baud, and the fastest commonly used baud rate is 19,200 baud. Asynchronous serial links use a variety of combinations of the number of data bits, what type (if any) of parity bit, and the number of stop bits. A typical combination is 7 data bits, even parity, and 1 stop bit. RS232/V.28 physical links are also suitable for synch- ronous transmission protocols. These higher level protocols often use the standard RS-232C/V.28 voltage levels. Note that one type of physical link (such as RS-232/V.28 voltage levels) can be used for a variety of higher level protocols. Table 2 summarizes the voltage levels and other requirements of V.28 and RS-232. Comparison of RS-232C/V.28 with other Standards The other two most commen serial interface specifica- tions are the EIA RS423 and RS422/RS485 (CCITT recommendations V0 and V.11). While the RS-232 or V.28/V.24 interface is the most common interface for communication between equipment made by different manufacturers, the RS423/V10 interface and RS422/V.11 interfaces can operate at higher baud rates. In addition, the RS485 interface can be used for low cost local area networks. The RAS423 and V0 interfaces are unbalanced or single-ended interfaces which use a differential receiver. This standard is intended for data signaling rates up to 100 kbit/s (100 kilobaud). It achieves this higher baud rate through more precise requirements 9-12 on the waveshape of the transmitters and through the use of differential receivers to compensate for ground potential variations beween the transmitting and re- ceiving equipment. With certain limitations, this inter- face is compatible with RS-232 and V.28. The limita- tions are: 1) less than 20,000 baud rate, 2) maximum cabie lengths determined by RS-232 performance, 3) RS423/V10 DTE and DCE signal return paths must be connected to the the RS232/V.28 signal ground, 4) the RS-232 transmitter output voltages must be limited to +12V, or additional protection must be provided for the RS423/V10 receivers, and 5) not all RS232/V.28 receivers will show proper power-off detection of V10 transmitter outputs. Maxims MAX230 and MAX232-MAX238, MAX240 and MAX241 meet restrictions 4 and 5 over the entire range of recommended operating conditions. The MAX231 and MAX239 meet restrictions 4 and 5 provided that the V* voltage is 12.5V or less. The RS422, RS485, and V.11 interfaces are balanced double-current interchanges suitable for baud rates up to 10 Mbit/s. These interfaces are not compatible with RS-232 or V.28 voltage levels. Application Hints Operation at High Baud Rates V.28 states that the time required for the signal to pass through the transition region during a change in state shall not exceed 1 millisecond or 3 percent of the nominal element period on the interchange cir- cuit, whichever is less. RS-232C allows the transition time to be 4 percent of the duration of a signal element. At 19,200 baud, the nominal element period is approximately 50us, of which 3 percent is 1.5us. Since the transition region is from -3V to +3V, this means the V.28 slew rate would ideally be faster than 6V/1.5us = 4V/us at 19.2 kbaud and 2V/us at 9600 baud. The RS-232 requirement is equivalent to 3V/ys at 19.2 kbaud, 1.5V/us at 9600 baud, etc. The slew rate of the MAX230 series devices is about 3V/ys with the maxi- mum recommended load of 2500pF. In practice, the effect of less than optimum slew rate is a distortion of the recovered data, where the 1s and 0's no longer have equal width. This distortion generally has negli- gible effect and the devices can be reliably used for 19.2 kbaud serial links when the cable capacitance is kept below 2500pF. With very low capacitance load- ing, the MAX230 and MAX234-239, MAX240 and MAX241 may even be used at 38.4 kbaud, since the typical slew rate is 5V/us when loaded with 500pF in parallel with 5kQ. Under no circumstance will the MAAIM+5 22k = TL INPUT PULLDOWN av ag-232 | wl (OTT XMTR t R8-232 > WIT *n NON-INVERTED TTL QUTPUT AVERTED TTL SIGNAL +OV of , -ov I I i Nv w Figure 17 Non-inverting RS-232 Transmitters and Receivers. slew rate exceed the RS-232/V.28 maximum spec of 30V/us and, unlike the 1488 driver, no external com- pensation capacitors are needed under any load con- dition. Driving Long Cables The RS-232 standard states that The use of short cables (each less than approximately 50 feet or 15 meters) is recommended; however, longer cables are permissible, provided that the load capacitance .. . does not exceed 2500pF Baud rate and cable length can be traded off: use lower baud rates for long cables, use short cables if high baud rates are desired. For both long cables and high baud rates, use RS422/V.11. The maximum cable length for a given baud rate is determined by several factors, including the capacitance per meter of cable, the slew rate of the driver under high capacitive loading, the receiver threshold and hysteresis, and the acceptable bit error rate. The receivers have 0.5V of hysteresis, and the drivers are designed such that the slew rate reduction caused by capacitive loading is minimized (see Typical Characteristics). MAXIM +5V Powered RS-232 Drivers/Receivers Non-Inverting Drivers and Receivers Occasionally a non-inverting driver or receiver is needed instead of the inverting drivers and receivers of the family. Simply use one of the receivers as a TTL/CMOS inverter to get the desired operation (Figure 17). If the logic output driving the receiver input has less than 1mA of output source capability, then add the 2.2kQ pullup resistor. The receiver TTL outputs can directly drive the input of another receiver to form a non-inverting RS-232 receiver. Protection for Shorts to +15V Supplies All driver outputs except on the MAX231, MAX232 and MAX233 are protected against short circuits to +15V, which is the maximum allowable loaded output voltage of an RS-232/V.28 transmitter. The MAX231, MAX232, and MAX233 can be protected against short circuits to +15V power supplies by the addition of a series 220 resistor in each output. This protec- tion is not needed to protect against short circuits to most RS-232 transmitters such as the 1488, since they have an internal short circuit current limit of 12mA. The power dissipation of the MAX230 and MAX234- MAX239, MAX240 and MAX241 is about 200mW with all transmitters shorted to +15V. Isolated RS-232 interfaces RS-232 and V.28 specifications require a common ground connection between the two units communi- cating via the RS-232/V.28 interface. In some cases, there may be large differences in ground potential between the two units, and in other cases it may be desired to avoid ground loop currents by isolating the two grounds. In other cases, a computer or control system must be protected against accidental connection of the RS-232/V.28 signal lines to 110/ 220VAC power lines. Figure 18 shows a circuit with this isolation. The power for the MAX233 is generated by a MAX635 DC-DC converter. When the MAX635 regulates point A to -5V, the isolated output at point B" will be semi-regulated to +5V. The two opto- couplers maintain isolation between the system ground and the RS-232 ground while transferring the data across the isolation barrier. While this circuit will not withstand 110VAC between the RS-232 ground and either the receiver or transmitter lines, the voitage difference between the two grounds is only limited by the optocoupler and DC-DC converter transformer breakdown ratings. 9-13 bbZ-OECXVNMAX230-241* +5V Powered RS-232 Drivers/Receivers Sv TO 5Y {SOLATED +5 _r] De - oc ISOLATED CONVERTOR *v |SEE FIGURE 19) 1 | 2 FE | . 03 | s 18 2 | $n Veo vr +a | Wy Tw Ttaut fla 10 |4nz6 ko | 5 GATE WITH ' | , 4mA OUTPUT | c+ SINK CAPABILITY + 1 2 | 4 =e I MAXIMA 3 ISOLATED ci- sy | ee MAX232 , ! o2+ + 2kn ance no 7) 5 ' rn ~<} <4 | | lt cp40108 Mc 4584 | (29 Blour Alm 93 RO TANCL4 4 | 2 | oR OTHEA | cmos SCHMITT TRIGBER | * = 8 SYSTEM BROUND | Tr ISOLATION AS-232 BARRIER SROUND Figure 18. Optically isolated RS-232 interlace. +5 INPUT 0 B +V5 MAXIA quiPuT MAX635 Mi 8 Vea OUT 100 uF Lal eND - TRANSFORMER: 1:1 TURNS RATIO 330,.H PRIMARY INDUCTANCE 9-14 Figure 19. +5V Isolated Power Supply For Optically fsolated RS-232 Intertace. MAAIM-+-5V Powered RS-232 Drivers/Receivers Ordering Information PART TEMP, RANGE PACKAGE |. PART | TEMP RANGE PACKAGE MAX230 0.3 Wide MAX236 0.3" Wide <f MAX230CPP 0C to +70C | 20 Lead Plastic DIP MAX236CNG | 0C to +70C | 24 Lead Plastic DIP MAX230CWwP | 0C to +70C | 20 Lead Wide S.0. MAX236CWG | 0C to +70C | 24 Lead Wide SO MAX230C/0 oC to +70C_| Dice MAX236C/D 0C to +70C | Dice MAX230EPP | -40C to +85C_| 20 Lead Plastic DIP | MAX236ENG | -40C to 85C | 24 Lead Plastic DIP MAX230EWP | -40C to +85C | 20 Lead Wide SO | MAX236EWG | -40C to -85C | 24 Lead Wide SO MAX230EJP | -40C to +85C | 20 Lead CERDIP MAX236ERG | -40C to *85C | 24 Lead CERDIP | MAX230MJP__| -55C to +125C | 20 Lead CEADIP | MAX236MRG | -55C to -125C | 24 Leag CERDIP _i| <[MAX231 0.3 Wide | MAX237 a _|03" Wide MAX231CPD 0C to +70C | 14 Lead Plastic DIP MAX2370NG | OC to +70C | 24 Lead Plastic DIP MAX231CWE | 0C to +70C_| 16 Lead Wide S.O. | MAX237CWG | 0C to +70C | 24 Lead Wide SO MAX231C/D OC to +70C | Dice | MAX2a7C/D | 0C to +70C_| Dice | MAX231EPD | -40C to +85C | 14 Lead Plastic DIP MAX237ENG | -40C to +85C | 24 Lead Plastic DIP MAX231EWE | -40C to +85C | 16 Lead Wide S.O. | MAX237EWG | -40C to +85C | 24 Lead Wide SO | MAX231EJD | -40C to +85C | 14 Lead CERDIP | MAX237ERG | -40C to 85C | 24 Lead CERDIP eT MAX2SIMID -55C to +125C | 14 Lead CERDIP JAMAX237MRG_ | -55C to ~125C | 24Lead CERDIP _| s | MAx232 0.3 Wide MAX238 | - 0.3 Wide MAX232CPE 0C to +70C | 16 Lead Plastic DiP | MAX238CNG | 0G to +70G | 24 Lead Plastic DIP__ MAX232CWE | 0C to +70C | 16 Lead Wide S.O | MAx238CwG | C to +70C | 24 Lead Wide SO. | MAX232C/D C to+70C | Dice | Max23ec/D | oCto+70C | Dee __=i! MAX232EPE | -40C to -85C | 16 Lead Plastic DIP MAX238ENG | -40C to +85C | 24 Lead Plastic DIP_| MAX232EJE | -40C to +85C_| 16 Lead CERDIP | MAx238EWG | -40C to 85C | 24 Lead Wide SO | MAX232EWE | -40C to +85C | 16 Lead Wide SO MAX238ERG | -40C to +85C | 24 Lead CERDIP. MAX232MJE | -55C to +125C | 16 Lead CERDIP | MAX238MRG___-55C to +125C | 24 Lead CERDIP <M Ax233 0.3" Wide MAX239 / 0.3 Wide MAX233CPP 0C to 470C | 20 Lead Plastic DIP | MAX239CNG OC to +70C | 24 Lead Plastic DIP__| MAX233EPP | -40C to +85C | 20 Lead Plastic DIP | MAX239CWG | 0Cto+70C | 24Lead Wide SO | <[Maxza4 0.3 Wide | MAX238C/D OC to +70C | Dice | MAX2340PE 0C to +70C | 16 Lead Plastic DIP MAX239ENG | -40C to +85C | 24 Lead Plastic DIP MAX234CWE | 0C to +70C | 16 Lead Wide S.0. | MAX230EWG | -40C to +86C | 24 Lead Wide SO | MAX2340/D 0C to +70C | Dice | MAX239EAG | -40C to +85C | 24 Lead CERDIP | MAX234EPE | -40C to +85C_| 16 Lead Plastic DIP MAX239MRG | -55C to +125G | 24 Lead CEADIP MAX234EWE | -40C to +85C | 16 Lead Wide SO. _ | MAx240 Flatpak MAX234EJE | -40C to +85C | 16 Lead CERDIP | MAX240CMH octo+70C | 44 Lead Flatpak si MAX234MJE | -55C to #125C | 16 Lead CEROIP | MAX2a0EMH | -40C to 185C | 44 Lead Flatpak <_ [max235 0.8 Wide ~ | MAX241 |0.3" Wide MAX235CPG 0C to+70C | 24 Lead Plastic DIP" Maxoatew | -ageg to ges. | be reag Wide SC MAX235EPG | -40C to +85C | 24 Lead Plastic DIP* MAX235EDG | -40C to +85C | 24 Lead Ceramic MAX235MDG -55C to +125C | 24 Lead Ceramic* * = 0.600 package MAXIM 9-15 bP S-OECXVN+5V Powered RS-232 Drivers/Receivers Table 1. Circuits Commonly Used for RS-232C and V.24 Asynchronous Interfaces Table 2. Summary of RS-232C and V.28 Electrical Specifications Receive Data (RD) Request To Send (RTS) Clear to Send (CTS) Data Set ready (DSR) Data from DCE Handshake trom DTE Handshake from DCE Handshake from DCE MAX230-241* N DOO fF WD Reference Point for Signals Handshake from DCE Signal Ground 8 Received Line Signal Detector PIN CIRCUIT PARAMETER SPECIFICATION COMMENTS 1 Protective Ground Connect to Driver Output Voltage Earth Ground O level +5V to +15V With 3-7kQ) load 1 level -5V to -15V With 3-7kQ2 load Transmit Data (TD} Data from DTE Max output +95V Max No Load Receiver input Thresholds (data and clock signais) 0 level +3V to +25V 1 level -3V to -25V Receiver Thresholds RTS, DSR, DTR On tevel +3V to +25V Off level Open Circuit Detects Power or -3V to -25V Off Condition at Driver (sometimes called Carner Detect, DCD) pocener Input 3k0 to 7KO 1 Printer Busy Signal Handshake from Printer 20 Data Terminal Ready Handshake from DTE oeioron Resistance, 22 Ring Indicator Handshake from DCE condition 3000 Min. Vout < *2V Driver Slew Rate 30V/us Max 3k < Au < 7k; OpF < C, <2500pF Signalling Rate Up to 20kbits/sec. 5015 m Longer cables Cable Length Recommended permissible, if Max Length Croan S 2500pF Vet GND Tiour Aum onre {1 628mm] + T | Co v- Taour Raw olay | (2.048mm) MAX231, MAX232 and MAX233 Note: Connect substrate to V*. Chip Topography Tout T4our R3quT - SHUTDOWN 0138 (251 mm) MAX230 and MAX234-239, MAX240, MAX241 Notes: 1. Shutdown pin of MAX234, MAX237, MAX238, MAX239. MAX240 and MAX241 are internally connected to ground 2 Connect substrate to V" Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product No circuit patent licenses are implied Maxim reserves the right to change the circuitry and speerfications without notice al any time 9-16 MAAI/VI