What IO port is the built in terminal/serial port

Discuss the new Altair 8800 Micro

What IO port is the built in terminal/serial port

Postby Corey986 » Nov Wed 14, 2012 9:40 am

I want to do a little dev work on a bootloader and need to know if the built in terminal and serial port are at IO ports 20/21 like a real MITS SIO2 port 0.

Thanks,
Corey
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Re: What IO port is the built in terminal/serial port

Postby lexthehex » Nov Tue 27, 2012 5:43 pm

Corey986 wrote:I want to do a little dev work on a bootloader and need to know if the built in terminal and serial port are at IO ports 20/21 like a real MITS SIO2 port 0.

Thanks,
Corey


The serial port is at 10/11h (i.e. 16/17 decimal) - 20/21 being octal. I wrote a program to test this. This was written in CP/M on in the AltairZ80 emulator in SIMH, but works identically on the Altair - or it should.

Code: Select all
A>type chrs.prn
 0100                   org     100h
 0100 060A      start   mvi     b,10
 0102 3E20      loop0   mvi     a,32
 0104 D311      loop1   out     11h
 0106 C601              adi     1
 0108 0E00              mvi     c,0
 010A 0D        loop2   dcr     c
 010B C20A01            jnz     loop2
 010E C600              adi     0
 0110 FE7F              cpi     7Fh
 0112 C20401            jnz     loop1
 0115 05                dcr     b
 0116 C20201            jnz     loop0
 0119 C9                ret


If you run it from another location, you'll need to change the addresses at 0x10C/0x10D, 0x113/0x114 and 0x117/0x118. 'loop2' is to stop serial port overruns, which happen if the code runs as fast as it can.

I haven't tried input yet; I think that you read a byte from port 11h, and if it is non-zero, it's an incoming byte.
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Re: What IO port is the built in terminal/serial port

Postby vbriel » Nov Tue 27, 2012 7:02 pm

Anything from the original Altair code for reading from the serial port will work. For example, the bootloader code is the same as the original, just built in, but yes your port #'s are correct. I'd like to work on a dual serial port card in the future, but I never have free time.
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Re: What IO port is the built in terminal/serial port

Postby waltermixxx » May Thu 07, 2015 4:45 pm

wondering about sense switch usage with the serial port,

http://www.solivant.com/altair_bootload ... rs&pagen=1

in the examples here for an original Altair 8800 the sense switches are used to enable different serial modes,
with the micro 8800 do we need to worry about the sense switches when reading and going through software examples
for the original?

please advise. :)

Thank you :)
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