PIC17C756 Market: Communication Telephone Line Cards Application Brief Line Card Monitor Processor P.O.T.S.* Main Telephone Network High Speed ISDN or DSL Link Mixed Signal ASIC 16 - 32 P.O.T.S.* USART 7 17C C I P 56AI/O Dial Tone I/O Connect/Disconnect P.O.T.S.* * Plain Old Telephone System APPLICATION DESCRIPTION In most commercial or residential telephone services, the final connection to the telephone exchange is made via a line card. Normally 16 to 32 Plain Old Telephone Systems (POTS) are connected to one line card, and in a given interchange, there may be a dozen or more line cards. Each line card essentially contains a mixed-signal, highspeed ASIC, which interfaces the POTS to highspeed ISDN or DSL lines connected to the central exchange. In most cases, the ASIC does a pretty good job in handling the interchange. However, as each ASIC is asked to handle more and more signals, the throughput drops dramatically. The main reason for the drop is the number of lines being used at one time and the different distances of lines from the line cards. The PIC17C756A was added to the line card to reduce some of the overhead of the ASIC. The PIC17C756A independently monitors the signal condition and the connect/disconnect condition of the POTS. This information is communicated to the ASIC via the USART, and the ASIC in turn takes direct action to compensate for a drop in the line or other conditions which may occur. Thus the line card essentially has doubled its capacity with the addition of a peripheral microcontroller, namely the PIC17C756A. The large number of I/O lines on the PIC17C756A can be used to monitor the POTS. The 12 channel A/D converter with 10 bit accuracy can monitor the POTS signal level and determine if additional gain needs to be applied to a particular POTS. The fast throughput of the PIC17C756A speeds calculations and monitoring of the I/O line and A/D converters. The USART is used for communications to the ASIC. PIC17C756 Market: Communication Telephone Line Cards Application Brief System Requirements System Requirements PICmicroTM MCU Applicability Interface POTS* to ISDN or DSL high speed telephone links and handle signal level, dial tone and basic connect/disconnect of POTS. * Fast throughput. The PIC17C756A acts as a co-processor on the line card to reduce load on Mixed Signal ASIC Must handle multiple lines (16 to 32 POTS) * 50 I/O lines to handle larger number of lines Must monitor signal strength and connect/disconnect condition * A/D converter to monitor signal conditions, i.e., signal strength, connect and disconnect condition of POTS Must have high throughput capability * USART to communicate directly to ASIC, resulting in faster throughput to handle line traffic Related Applications * Other Telecom PIC17C756A Features Performance Peripherals Power Package DC - 33 MHz 4 Captures (16 bit) BOR DIE Program Memory: 16K internal, 64K external 3 PWM (10 bit) < 1 A Standby Current 64/68 pin Data Memory: 902 bytes 4 Timers Single Cycle Instructions 2 USARTs 8 x 8 Single Cycle Multiply in 121 ns 10-bit A/D (12 channel), < 1LSb error Low Voltage Capability - see the PIC17C75X Data Sheet for details (DS30264A) SPITM I2CTM Master Watchdog Timer Key features utilized in this application. (R) Microchip Technology Inc. * 2355 West Chandler Blvd. * Chandler, AZ 85224-6199 U.S.A. (602) 786-7200 * FAX (602) 899-9210 * Technical Support (602) 786-7627 Web Site: www.microchip.com The Microchip name and logo are registered trademarks and PICmicro is a trademark of Microchip in the USA and other countries. All other trademarks mentioned herein are property of their respective owners. Information subject to change. (c)1998, Microchip Technology Inc. All rights reserved. DS30602A_3