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RS232 Programming

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I seem to have this RTS/CTS thing working however to make it work I had to make CTS logic high to hold of the PC from sending. I thought it would the reverse. (?)


Here is the code primitive that checks for a key and leaves in R4 (TOS cache) if it finds one.

(in RPN assembler of course) :)


Configuration is held in variables:

CARD contains >1300 

UART contains CARD+>40   (or >80 for RS232/2)

CODE: CKEY? ( -- n )          \  "com-key"
         0 LIMI,
         R12 RPUSH,           \ save R12 on return stack
         CARD @@ R12 MOV,
         5 SBZ,               \ CTS line LOW. You are clear to send
         TOS PUSH,            \ give us a new TOS register (R4)
         TOS CLR,             \ erase it
         UART @@ R12 MOV,     \ select >1340 CRU address
         21 TB,               \ test if char ready
         EQ IF,
             TOS 8 STCR,      \ read the char
             18 SBZ,          \ reset 9902 rcv buffer
             CARD @@ R12 MOV,
             5 SBO,           \ CTS line HI. I am busy!
             TOS SWPB,        \ shift to other byte
         R12 RPOP,            \ restore old R12
         2 LIMI,

For the curious...

This primitive routine is then used in the Forth kernel to make the "keyword"  KEY which waits for a key (forever) and returns it if CKEY? returns a non-zero

: KEY       ( -- char)
              PAUSE        \ multi-tasking switch
              CKEY?        \ test for key
              ?DUP         \ dup if not zero
            UNTIL          \ loop until not zero on stack
            83D6 OFF ;     \ reset VDP screen timeout

Now when I paste source code into Tera term it stops at the end of a line automagically until the compiler has digested the code and then continues.

Before I had to put a 300ms delay in Teraterm to prevent over-running the Forth compiler.

I still need a 1mS delay between characters because Forth echoes each character back and without a receive interrupt I can't do duplex but it's better than it was.


I am pleased.

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