Apple IIe DIY Serial Card?

[thenzero]

I know I know. Life and a million projects gets in the way, but it’s still on my workbench. Maybe this weekend.

 

[VERAULT]

I am guilty of the exact same thing. Dont worry I just wanted to put a pin in it.

 

[epooch]

The EEPROM is probably the most expensive single component.
Jameco Shopping Cart
…

Part Number, Description, Quantity, Unit Cost, Total
74843,"IC,EEPROM,28C256-15,5V 32kx8,D","5","$12.25","$61.25"

Those are expensive EEPROMs. You can bring the price down a bit by using:

28C16A-25 EEPROM Memory | Jameco Electronics

Jameco Electronics 28C16A-25 EEPROM. Products in stock and ready to ship. Quotes, samples and datasheets available at Jameco Electronics.

www.jameco.com

250ns seems slow, but some of the Apple cards have 400ns ROMs, I think.
And AT28c64 EEPROMs are dirt cheap on eBay. 5 for $6.00.

 

[VERAULT]

Thats good to know thanks epooch.

 

[bitfixer]

You might be able to omit the MAX232 chip, given the high likelihood of using a usb->serial adapter from a modern computer instead of a true serial port. Just a cost saving idea.

 

[Eudimorphodon]

You might be able to omit the MAX232 chip, given the high likelihood of using a usb->serial adapter from a modern computer instead of a true serial port. Just a cost saving idea.

They only cost a couple bucks, and in their capacity as a buffer there's at least a chance they'll throw themselves on top of the landmine and stop a stray short or spark from getting to the more expensive 6551, so... doesn't really seem worth it. (And of course this is on top of limiting yourself to TTL-level serial.)

Those are expensive EEPROMs. You can bring the price down a bit by using:

If you're making your own thing that doesn't specifically require an EEPROM (IE, you're not writing to it in-circuit, you just need a programmable ROM) I would highly recommend subbing a 32 pin socket wired to use an SST39SF010 flash chip. They're dirt cheap ($1.67 quantity one at Mouser) and rated for 70ns so speed shouldn't be a problem on any "antique" computer. (I've used them for video character generators, they work fine for that.) Yes, they're 128K and you're wasting most of it, but just tie those extra address pins to ground and you're good to go.

 

[VERAULT]

i use a true serial device with my ssc so cutting this corner i think would not be worth it. Backwards compatibility is the name of the game.

 

[VERAULT]

@thenzero Its been since march cummon! Im eager to try my own build but wanted to know how your build went.

 

[thenzero]

 

[VERAULT]

ABANDONED

 

[thenzero]

Never! Just delayed a bit

 

[btb]

I built one of these and it worked great. Well, actually I built one that I redesigned somewhat:



The main change is that it uses 1488/1489 driver/receiver chips that the original SSC used, instead of MAX3232s, which are more expensive and require a bunch of electrolytic caps. If you use the CMOS version of the 1488 you don't even need the 3 330pf slew capacitors.

There's not much updated info here, but there are kicad files and gerbers:

GitHub - btb/ssc: A slight rework of jmthompson's ssc

A slight rework of jmthompson's ssc. Contribute to btb/ssc development by creating an account on GitHub.

github.com

I've only tested it in ADTPro.

Turns out that the GAL is only replacing 4 or 5 discrete logic chips, so I'm also working on a version that doesn't need the GAL and still fits into 100mm.

 

[skate323k137]

The guy who created the simple clone omitted the DIP switches, so the port config won’t be a given. He said that he would upload a ROM with a set config, but I don’t see one, yet.

- Alex

Presuming this hasn't been updated... in the absence of DIPs (and bootstrapping aside), does the card work at multiple baud rates as long as both softwares are configured the same? Or is the current ROM at a fixed baud rate?

I don't use bootstrapping so these might be nice for wimodem232 usage.

 

[thenzero]

Holy cow that's amazing btb!

 

[agentb]

What a great project, looking forward to seeing your further iterations and some others building this too. I don't have a SSC for my Apple IIe so certainly would like to try one of these in the future.

 

[btb]

I'm not very familiar with the usage of the switches on the SSC, and the manual is not terribly direct. If I could squeeze a handful of switches onto a revision of my card, which ones are useful?

 

[btb]

Ah, I see the problem now described at https://github.com/jmthompson/ssc/issues/1 - I already had a disk, so I didn't need to bootstrap ADTPro, but this is something that i suppose should really be fixed.
Before I dive too much into the firmware, does anyone have insight into this problem, which is almost certainly related to getting bad data when trying to access the card's switches/"registers"

 

[Eudimorphodon]

I would suspect the specific ”freezing” issue relates to the switch settings that enable/disable keyboard and/or screen I/O when using the built-in software. But of course all the settings are going to be read as whatever the bus floats to in an Apple II (usually “high” unless there are specific pull-downs) so I would wager the effective defaults are never going to useful.

 

[VERAULT]

Well im out as bootstrapping is a necessity for me. I rely on adtpro bootstrapping almost exclusively so I dont have to deal with boot disks.

A novel cards but not a replacement to the SSC.

 

[btb]

Now I'm thinking that the SSC is so devilishly simple already, there's probably not going to be a workaround that's any easier than just making it a full clone with the switches and all. Could leave out the jumper block but that might be about it.

for a low parts-count version, you can modify the firmware and be slightly incompatible - ooorrrrr I think one could put the switch settings in a couple unused bytes in the EEPROM, and there might be just enough free pins on the GAL to put in the select logic for it. (you also have to make sure to merge the CTS bit into the SW2 byte)