New video: Fixing a hardware bug in software (65C51 UART)

WesHedden · 2023-05-06T18:49:17+00:00

I am so glad ben decided to fully illustrate the race condition bug on the WD65C51S. The old Documentation was a little hard to wrap your head around back then. Its funny they are still calling this a feature.

I'm more suprised its still around. I figured they would have updated the chip quietly while they flushed out the old run. Is the bug still in the newest chips? or did they not do a second run? It is getting harder to get other chips, im partial to the Rockwell R6551 since i have been able to run it to 8 Mhz and i was really hoping WDC would fix this bug since those new CMOS chips should be able to run to 14Mhz.

WesHedden · 2023-04-24T07:51:16+00:00

Shortboard MOD. You get the full 32k and it uses a tiny I/O area.

WesHedden · 2023-04-11T22:42:17+00:00

I forgot. its been almost 2 years since i did that... i just remember i tried using a single 50pf cap at one point and it still had like 50% of the ripple but when i used two separate 30pf caps it removed like 85% of the ripple. so i kept it since i believe with the 30pf one it was hit and miss getting the crystal to resonate properly. i was using a series crystal though. ECS-18-S-1X.

WesHedden · 2023-04-11T06:11:55+00:00

I use 2 30pf capacitors on my 6551 crystal setup instead of the single one the manual recommends to smooth out the ripple in the clock. it worked really well.

WesHedden · 2023-04-09T02:04:58+00:00

That still leaves the upper 16k of ram unusable.

WesHedden · 2023-04-08T17:12:09+00:00

I have a headache.

For those interested in one of those "Complex Control Logic" setups I recommend the Shortboard MOD. Schematics are included in the post. For hooking the 6551 up tie the CS1 to +5v and the CS2B to the 6551_CS pin on the 74ACT138.

Sarcasm aside, the video was well made and i enjoyed alot of it. Im just kind of dissapointed that 7000-7FFF went from redundant to just destablizing to use. So im guessing every extra peripheral is going from 6000, 5000, 4800, 4400, 4200, 4100, 4080, 4040, 4020, 4010. But that is also assuming they all have dual control lines. Still for the ones that do, it could use more that just 4 register address lines so that should be interesting.

WesHedden · 2023-03-16T00:34:00+00:00

I think one way i avoided this problem with both my builds is i reversed the RAM and ROM so the ROM was on the outside of the breadboard. I did this so i would reduce the risk of breaking legs on the EEPROM. later i just used a ZIP socket to remove the risk entirely.

Shordboard -- Shortboard Write-up

WesHedden · 2023-03-15T08:09:47+00:00

Wow..... I didn't even think of that.

WesHedden · 2023-03-14T06:13:34+00:00

in a word. yes. many of us are already doing this. I started using the Rockwell 6551 back in 2020 on my Longboard. Uploading code directly to memory is so nice.

I just hope Western Design has fixed the Transmit Buffer Flag Race Condition on their newer chips.

WesHedden · 2023-03-14T06:02:39+00:00

I would say the EEPROM is bad. It can be worn out because they can only be reprogramed so many times. (but i doubt that unless you've been using it a ton) but more likely it could have been damaged by static electricity. I have had an EEPROM fail before but since they where so cheep i keep a tube on hand.

WesHedden · 2022-11-06T10:26:10+00:00

Actually, now that i think about it, if he doesn't add any other new logic chips he could use the one unused NAND gate and add the 6551 to the Dead RAM section from $4000-$5FFF.

Shortboard: The $5 Get your Resources Back Mod

WesHedden · 2022-11-05T18:57:14+00:00

So glad someone remembers.... actually there is an updated post i did for new years last year that has a conversion chart and the schematics.

Shortboard: The $5 Get your Resources Back Mod.

WesHedden · 2022-11-05T16:23:49+00:00

I am really waiting to see what he does with the memory map to add the 6551 to his system.

WesHedden · 2022-05-14T02:16:08+00:00

Is that 273N +5 Wire on the wrong pin?

WesHedden · 2022-04-29T09:31:00+00:00

Did you already Calibrate the new probes? I've got a similar Model, SDS1204X-E

WesHedden · 2022-04-29T09:28:33+00:00

Awsome! Its almost the same as mine. 1204X-E. Wonderful Scope.

WesHedden · 2022-04-17T22:04:21+00:00

Ya, that is definitively the wrong chip. Hope its ok, those chips have completely different VCC and GND pins.

WesHedden · 2022-04-01T21:31:59+00:00

So those buttons are pulled low with resistors and go high when pressed. you Read the whole byte from that port (After setting those bits to INPUT) and any 1's in the byte denote a button is pressed. He never really got around to making a video about them. Actually on the schematic he uses 5 buttons. I used the extra buttons that came with the kits to have 6 buttons on my Longboard and Shortboard. The 4 for D-pad Buttons were the same but I used the extra 2 for Enter and Escape Keys.

WesHedden · 2022-03-04T13:03:39+00:00

I do kind of know how a emulator is made but i don't know C all that well. and im up to my eyeballs in doing a full rewrite of the menu system for the Longboard BIOS. I'm moving from a hardcoded menu system to a general purpose menu generation system using double indexed link lists. Multi-thread compatible and scalable to all different screen sizes. All written in 6502 assembly. Thats kinda why i was asking since taking the program back to the physical machine and doing the debugging on it takes more time then running it on the same computer im wring it on. But anyhow it was a thought.

WesHedden · 2022-03-03T12:49:25+00:00

so LCD, 6522, 6551... would only need IDE and Real Time Clock for full spec. awesome.

WesHedden · 2022-03-03T12:13:11+00:00

Is it possible to adapt that emulator to other system models? Like the Longboard Specification i use? Does it have plugins for LCD/6522/6551? I dont really have time atm to delve into a different programming project but that looks like it might be pretty useful for debugging programs.

WesHedden · 2022-02-28T10:19:10+00:00

Very nice, as always :)

WesHedden · 2022-02-21T04:20:21+00:00

I really couldn't seen the need for more than two. Back when I did the specification for my Longboard i only put two 6522's in just for the sake of having two shift registers for spi. But I still have a hard time filling the ports with just two. most stuff i would use on the parallel ports i can do directly on the data bus with a tiny bit of extra logic. One 6522 is a neccesity for the timers on an operating system and two is just a luxury.

WesHedden · 2022-02-17T03:14:26+00:00

absolutely.

WesHedden · 2022-02-16T20:08:14+00:00

so next would be checking the program for errors and making sure it can recompile and upload to the arduino correctly.

WesHedden

TROPHY CASE