i8355 from SDK-85 flakey
ard at p850ug1.demon.co.uk
Wed Apr 28 13:46:20 CDT 2010
> And Tony, you are correct on the serial interface. It is sourced by the
> SOD pin of the 8085 and then a single transistor drives the current loop.
It was Allison who said it used the SID and SOD pins of the 8085. However
this agrees wit hthe schematic in the book I have.
I can't find the links that Allison mentioned to seleect TTL/current
loop/RS232 mode. So either there are 2 versions of the board or my
scheamtics are 'simplified'. The only lionk I can see selects whether SID
comes from the current loop interface or is held low. If I am reading the
monitor lisitng correctly, then the bit of code starting at 0x0049 checks
to see if the SID pin is high or low. If the former it assumes a working
current loop device is connected (idle state would be to have the Tx loop
complete. so Q1 would be turned on, so SID high) and runs the teletype
monitor, if the latter, it runs the keypad/7-seg display monitor.
It's possible I've totally mis-uderstood this, I am not really a
programmer, and I've only just started looking at the SDK-85 monitor
> You need to invert this before feeding into a 1488 or equiv RS232
> driver but that's no big deal. All the TTY I/O runs at 110 baud,
I suspect you could use the current loop output trransistor as this
inverter (see my previous message). And I suspect that if you buffered
the RS232 output from you PC (using, say, a 1489), and fed that into the
current loop input -- pin 12 of J7 -- and cut R1 :-) then that would work
too. Or invert the output of the 1489 (say using a '04 -- or even another
secion of the 1489 as a kludge :-)) and feed it into the SID pin of the
8085 with the link S25 totally removed.
I would think that 110 bard would be trivial to do, and for the amount of
data you need to transfer, not a real problem. The monitor is 2K, 110
bard is 10 characters/second, so that's just oaver 200 seconds. Under 4
> timed by busy loops in the firmware but that's not a problem either.
> There's a routine in the ROM called "co" which will bit-bang chars out
> the interface as well as one called "nmout" which outputs ascii-hex bytes=
Or you could run the tty monitor and use the 'D' command to dump the
approrpatie area of memory (0 to 7FF I think). Capture the incoming data
on the PC (I think any reasonable terminal progam can do that -- C-Kermit
certainly can) and write a simple program to decode the hex dump back to
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