Modifications to Xerox 820-1 for Packet Radio Operation Page 1 This document presents the modifications to the Xerox 820-1 board which are necessary to use the KE3Z SIO-modem interface. The "top" of the board is the component side. 1. Cut the trace between pins 11 and 12 of the SIO (U96) on the bottom of the board. This may have already been done on some boards (it was on mine). [This separates the channel A RX data input and the SYNC output.] 2. Cut the trace between pin 29 of the SIO (U96) and the thru-hole on the top of the board. [This disconnects the channel B SYNC output from the RX data.] 3. Cut the trace between pins 28 and 29 of the SIO (U96) on the bottom of the board. [This disconnects the SYNC output and the RX data input.] 4. Cut the trace between pin 17 of the baud-rate generator (U97) and the thru-hole on the bottom of the board. [This breaks the path between the baud-rate generator and the SIO port B clock input.] 5. Connect a wire on the bottom of the board between pin 8 of U95 and pin 28 of the SIO (U96). Use the thru-hole connected to pin 8 of U95 for one end of the connection. [This reconnects the port B RX input to the RX data.] 6. Connect a wire on the bottom of the board between pin 17 of the baud-rate generator (U97) and pin 24 of the printer connector, J3. [This brings the port B 16x clock out to the interface.] 7. Connect a wire on the bottom of the board between the thru-hole which was connected to pin 17 of the baud-rate generator (U97) prior to step 4 and pin 17 of the printer connector, J3. [This brings the 1x clock from the interface to the SIO.] 8. Connect a wire on the bottom of the board between pin 24 of the modem connector, J4, and pin 32 of the J9 plug header. [This brings the port A 16x clock to the interface.] VERY IMPORTANT! You MUST perform the following jumpering before applying power to the board to ensure that no EIA levels are placed on the baud-rate generator outputs. Remove all jumpers on J9 on pin numbers 29 and above. Jumper J9-30 to J9-31. These pins are NOT across from one another on the header. Use wire-wrap to connect them. Jumper J9-33 to J9-35. These pins are adjacent, not across, but can still be jumpered with a standard header jumper. Make absolutely sure that J9-29, J9-34, J9-38 and J9-39 are not jumpered to ANYTHING. The following jumpers make the modem connector appear as a DCE. I know this seems bass-ackward, but it is done to make the modem connector the same "sex" as the printer connector, which is hardwired as a DCE. The interface board schematic assumes this to be the configuration. Modifications to Xerox 820-1 for Packet Radio Operation Page 2 Remove all jumpers from J9 pins 1-28, inclusive. Jumper the following pins across J9: 5-6 9-10 13-14 17-18 21-22 25-26 The following modification is optional. It connects power supply voltages to the modem connector for use by the interface board. Some people may be squeamish about this, so use your own judgement. Of course, you already have TTL clock signals on the RS- 232 connector.... 1. Connect a wire on the bottom of the board between +5 volts and J4 pin 18. +5 volts is available at pin 14 of U112. 2. Connect a wire on the bottom of the board between +12 volts and J4 pin 16. +12 volts is available at the end of R68 nearest J3. 3. Connect a wire on the bottom of the board between -12 volts and J4 pin 14. -12 volts is available at pin 1 of U111. Ensure that the modem connector is the one plugged into the interface board connector at P1-1 thru P1-25 to get the power connections. Although this interface board was developed for use with the multi-port repeater, it should work equally well with the KA9Q TNC software. I haven't had a chance to test that yet, but I am using a functional equivalent (same state machine etc.) on my S-100 system running Phil's code. DE KE3Z