SBC 2.5 availability/order?

[Martin_H]

I worked on the board this weekend and made good progress. Along the way I encountered a few small problems. So I continued with things I did understand and made a note of the problem. Here they are:

R301 is listed as a nine pin resistor array in the parts list, but there's only eight holes in the board. Do I clip the last lead to mount it?

R101 is not in the parts list. Is this array the same as R301? Note that there are only eight holes in the board here as well.

74hc21 does not have the dip-14 in the footprint column, so I didn't order a socket for it. Adding that I would help the ordering process.

D201, D401, and D501 look like they mount vertically. The silkscreen doesn't show the polarity, but the right square solder pad indicates to me that the black band should be soldered to the right side and the other lead to the left.?

Thanks,
Martin

[RichCini]

Martin_H wrote:

R301 is listed as a nine pin resistor array in the parts list, but there's only eight holes in the board. Do I clip the last lead to mount it?

This should be a 3.3k 8-pin array. I bought 8-pin ones on eBay but if you bought 9-pin ones you can cut off the last pin. Or, you can make an array with discrete resistors. I corrected the parts list and changed the Digikey part number. I think at some point I had intended on using a 9-pin array but wound up needing too many resistors so I used two 8-pin ones.

Martin_H wrote:

R101 is not in the parts list. Is this array the same as R301? Note that there are only eight holes in the board here as well.

Same as above. 3.3k RPACK.

Martin_H wrote:

74hc21 does not have the dip-14 in the footprint column, so I didn't order a socket for it. Adding that I would help the ordering process.

Done.

Martin_H wrote:

D201, D401, and D501 look like they mount vertically. The silkscreen doesn't show the polarity, but the right square solder pad indicates to me that the black band should be soldered to the right side and the other lead to the left.?

The reason for this is that if you use the old Rockwell or MOS 6522's, you don't need the diode (although there's no real reason to use the old MOS ones unless you have boxes of them). The square hole is to signify the band on the diode.

Thanks for picking up these inconsistencies in the parts list.

[Martin_H]

Thanks Rich, I was pretty sure those were the correct actions. But I figured "check twice, solder once" while assembling will reduce pain later on.

[RichCini]

Martin_H wrote:

Thanks Rich, I was pretty sure those were the correct actions. But I figured "check twice, solder once" while assembling will reduce pain later on.

That's pretty funny. I totally agree, though. I've always meant to buy a real rework station but I don't need it often (thankfully).

[Martin_H]

Digikey had another six pin DIN connector in stock, so I ordered it, the resistor network I was missing, and a PS/2 keyboard connector. I also received two Rockwell 6522's and a 6551 pulled from an old system for low cost off eBay. Hopefully they're working as claimed, although I've generally had good luck with used components.

I finished assembling the board, cleaned off the flux, and examined the board with a magnify glass. It doesn't look like I bridge any connections, but two of the solder joints looked sketchy, so I touched them up. Tomorrow I will put all the IC's in their sockets, and install the shorting jumpers. The mem cfg makes sense, and I think I use no handshake to talk to a PC.

@Rich, what are the /SO, BE, and ACIA null for?

[Martin_H]

Now that I programmed an EEPROM I plugged it into my SBC 2.7, plugged the SBC into a 9" B&W CRT TV, and turned it on. I plugged the COM port into my serial port and via trial and error determined that 19200 was the correct baud rate.

Good news. It turns on and displays the power on screen.

Bad news. The startup screen seems to hang on a blinking underscore character. Although one or two times it did enter EH BASIC on power up. Not sure what's up with that, but it might be electrical noise from the CRT, or maybe one of the chips is a bit flakey.

Good news. If I hit the panic button I enter the machine monitor. This seems to work fine and I can dump memory and examine registers. I then find the ? command and locate the command to cold start EH Basic. This seems fairly reliable.

Better news. After the cold start the systems seems fairly stable. I've entered simple programs and run them.

The next steps will be learning how to use the 6522's to do input and output like you do with microcontroller pins. I figured turning an LED on and off would be a good place to start. I'll also look at the source and see what the system is supposed to do on boot.

Down the road I'd prefer keyboard and mass storage connected to the machine. Using one computer to use another just doesn't seem proper.

[RichCini]

Great news Martin! Congratulations on getting it working.

Ideas for the keyboard -- if you can get/make a parallel ASCII keyboard, you can use one of the spare 8-bit input ports for it.

On the mass storage, the board has a Serial IEC interface. You could get an SD2IEC adapter and use that. I confess I never tried it, but I might order one and see if it works properly (I have the connector for it on the board).