Ken Websters PIC16C74 serial port multiplexer.

This code was developed by Ken Webster for his Time Source Monitoring Test System

14-bit core PIC source:

• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/sermux/sermux_m.asm (cached 20000106) Master: This is code for the PIC16C74 which is connected to the SRAM as well as all the other (slave) processors. It is responsible for reading and writing from/to the other processors, buffering data in the SRAM, and packaging and unpackaging data to/from routing packets.
• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/sermux/sermux_s.asm (cached 20000106)Slave: This is code for the PIC16C73s which act as smart buffered UARTs for the main PIC16C74 processor.

PC Windows NT or 95 or 98 source to talk to PIC:

• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/monitor/MultiplexerInterface.cpp (cached 20000106)

Uses CRC and checksum and packet serial number to detect corrupt or missing packets. Chop out code that supports channels if you only need one device connected (this app is for connecting multiple devices via a multiplexer). If need help feel free to email me at ken@webster.org

; Apply W to command-interpreter receive checksums
update_crx_checksums    xorwf           rCmdxs,F          ;update plain checksum
                        xorwf           rCmdcl,F          ;update cyclic checksum
                        addwf           rCmdch,F
                        bcf             STATUS,C
                        rrf             rCmdch,F
                        btfsc           rCmdcl,0
                        bsf             rCmdch,7
                        rrf             rCmdcl,F
                        movlw           0x31
                        addwf           rCmdcl,F
                        btfsc           STATUS,C
                        incf            rCmdch,F
                        movlw           0x03
                        addwf           rCmdch,F                        return

void Checksum::Add(unsigned char c){    plain_checksum ^= c;
    cyclic_checksum ^= c;    cyclic_checksum += (unsigned short)c << 8;
    bool carry = (cyclic_checksum & 1) ? true : false;    cyclic_checksum >>= 1;
    cyclic_checksum |= carry ? 0x8000 : 0;    cyclic_checksum += 817;}

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