Hey all!
This is my second attempt at building a 6502 based computer. My last attempt was not very succesful so I still consider myself very much a newby.

At the moment my computer consists of a 65c02 CPU, 32k ROM (AT28C256) and a 6551 ACIA.
I am using the memory map recommended in the primer found on 6502.org.
Before hooking up the ACIA I performed a NOP test by filling the rom with EA and pointing the cpu to the start of the rom, letting it count through all the adresses to confirm my rom was hooked up correctly.
Then I added the ACIA to my build, and this is where i'm at now.
To recieve this serial data I have an ftdi friend (https://learn.adafruit.com/ftdi-friend/overview) which supports rts and cts, so i hooked up those to my serial header accordingly (crossing over the signals). I did the same for the data lines. The other handshaking lines dtr, dsr and dcd I pulled low.

Before adding more to my computer I would like to test what I have built. I think the best way to do this is to write a simple program to the rom that initializes the ACIA, and transmits some text over serial, 'Hello world' for example .
I am just starting out learning 6502 assembly, so I'm a bit lost as where to start. I understand I need to write to the byte to the control register of the ACIA to initialize it, and then I need to write the byte for each letter of my message to the transmit register.

So my question then: Can anyone point me to a good source to learn more about programming the acia. Or can anyone help me in writing the code I described.
Thanks

Edit: I added a picture

You're welcome to try my Micromon monitor code. It will initialize and setup a full duplex interrupt-driven and buffered BIOS for the 6551. The monitor has enough features to be quite useful. It's also small... about 1.75KB in total.

_________________
Regards, KM
https://github.com/floobydust

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Hey, thanks for the responses!

[quote GARTHWILSON]
My RS-232 primer has a few paragraphs about 30% of the way down the page about a bug in the WDC W65C51N, discovered by forum member floobydust (who posted above while I was writing), in that the transmit-register-empty bit is stuck in the "on" state, meaning you can't use it to see when it's safe to hand the ACIA another byte to transmit. There's a link there to the topic, and to forum member GaBuZoMeu's excellent work-around which uses PB6 of a 65c22 VIA. My workaround used a VIA timer, but his is better.
[/quote]

Hey, thanks for the responses!


I read about that in your primer, but i am using the R6551AP, does this chip have the same bug?



I feel like i should go and read that one too... oops

After posting this i also came across this article which i found very helpfull: https://www.atarimagazines.com/compute/ ... 1_ACIA.php,
I'm going to try to adapt the code there to try on my machine.
With the help of the tables in that article i found that for an 8 bit word with one stop bit and no parity at a baud rate of 9600, the command register needs to have either $C2 or $82, and the control register needs $1E, is this correct?

(I was having a hard time with the post editor as you can tell )

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?