505 board converting to serial output

[nama]

Hi, I want to temporarily mod my 505 board to do serial output. I want to test the board before committing to building up a 540 replica board. the ultimate goal is to build a little video system.

Can anyone please confirm what is required?
I found this (see attached) in the back of the 505.pdf, but it's very hard to tell what exactly it is showing as the quality is so bad.
Beyond modifying the board, are there any other steps needed?

Thanks!

Screenshot 2024-02-22 at 8.27.24 AM.png (720.99 KiB) Viewed 588 times

[nama]

Just a follow up to my own post.
I believe this is correct. Please let me know if I've made any mistakes.

serial 505.png (37.35 KiB) Viewed 581 times

[nama]

Me again. I haven't had this 505 board working before, so thought I'd map out the jumpers as they presently exist.
The ROM installed is SYN600, and I think this is how it is presently set up.

505 jumpers.png (90.15 KiB) Viewed 569 times

[bxdanny]

If it's a SYN600 ROM, you aren't going to be able to make it a serial system without changing that, because the SYN600 doesn't include the 65A serial monitor.

Edit: I made up a file consisting of the SYN600 ROM but with the 65V monitor for 540/542 (relative page 2) replaced with the 65A. If you can burn this to a 2716, you can install that in place of the existing SYN600 ROM and not have to make any changes to the board, other than changing the signals to pins 20 and 21 of the ROM as needed by the 2716 (21 to ground instead of +5V, 20 to pin 3 instead of pin 4 of U4E, as provided for on the board).

[The .ini extension is to satisfy the forum's requirements for file extensions, but it's a straight binary ROM dump.]

[nama]

wow...brilliant.
That really saves me the hassle of re-jumpering this board, and avoids the the possibility of any board damage. I have a 2716 that I'll burn this weekend. I'll build up the backplane, wire everything up and see if I can do a power on test. Will let you know how I get on.

[nama]

I burnt the 2716 EPROM, lifted pins 20 and 21 out of the socket and jumper these to pin 3 U4E and GND respectively. I installed a 527 RAM board and rewired is as follows:

W3->F9 pin 15 (Y3 = $0000)
W1->F9 pin 14 (Y1 = $2000)
W2->F9 pin 13 (Y2 = $4000)

The 505 board looks to be modded for 9600 baud.
I hooked up a reset button, connected the serial to my Windows PC and powered it all up...no output to the terminal unfortunately
Tried a variety of baud rates, and null modem adaptors...no go.

Probing the TX line shows no activity on reset.

Things are pulsing on the board, but it all looks too regular, like no code is running. It's late here now, so I'll pick this up again tomorrow.

Cheers

[bxdanny]

Oops, there's a third change needed for the 2716, which I missed. Pin 18 of the ROM has to go to pin 14, rather than pin 15, of U2C (74148). All three changes are shown on sheet 2 of the 505B schematics found on Mark's site, and (I think) all have what are sometimes labeled as "W" points for doing cut-and-jumper changes (although that label isn't used on this schematic). BTW, any idea what the "W" is supposed to stand for?

[nama]

Much thanks for the info. Having a look at the mod on the 505B schematics I just wanted to revise a few things from what you had previously mentioned. So the complete mod seems to be:

- Pin 21 to ground instead of +5V (as mentioned)
- Pin 20 to pin 1 of U4F (not pin 3 of U4E)
- Pin 18 to pin 14 of U2C (as mentioned)
I think that is correct.

In fact, once I knew the correct mods, I could see these mods were already done on this board...so why an original SYN600 ROM was installed is a bit of a mystery!!!

Anyway, it still doesn't work!!!
Not getting any pulse out of the TX line (pin 6 of U1D 6850) on reset.

[nama]

Finally some success!
I came across this post from Dave talking about DCD and CTS lines:

viewtopic.php?f=3&t=190&p=1000&hilit=505+serial#p1000

I didn't hold much luck, but it worked!
Going to try and load a memory test program and see if anything is up with this 527 board.
Will report back.
Thanks!

423455194_1870844606751082_1767900542436278968_n.jpg (64.18 KiB) Viewed 522 times

[nama]

Yep...some very weird memory issues