Using a 6540 Adapter

[dansretropod]

Hi All,

Has anybody had any experience with these adapters:

http://store.go4retro.com/6540-adapter/

I bought a couple for a 2001 PET but cannot seem to make them work. I have downloaded the character set ROM from zimmers "characters-1.901447-08.bin" and have used an eprom burner to put it onto a 2764 eprom (I have verified the data is on there), placed the 2764 into the 6540 adapter and then placed it in the PET rom socket for the characters.

When I turn it on I just get a White screen with a flashing cursor, which would suggest it's reading in a load of zero's instead of the data

Am I doing something wrong??

Thanks,

Dan

 

[dave_m]

Dan,
If the data is in the lower 2K address space, have you properly grounded all the upper address lines? Or try to repeat the 2K pattern in all the 8K EPROM space as a test.

 

[MikeS]

I've used 3 or 4 of those adapters without problems; as a matter of fact, with a few jumpers I managed to put all 8 ROMS of both BASIC 1 and 2 into one and select the version with a jumper.

1 - Where in the 8KB address space is your 2KB ROM image?
2 - What jumpers/connections to the header are in place on the adapter, if any?
3 - Check Vcc and Vpgm on the 2764.
4 - Is it the old version or the new one? Is the '138 a DIP or SMT version?

 

[dansretropod]

Dan,
If the data is in the lower 2K address space, have you properly grounded all the upper address lines? Or try to repeat the 2K pattern in all the 8K EPROM space as a test.

Hi Dave,

Thanks for the advice, I duplicated the 2k across the 8k space and it worked. On the board are holes A11-A15, so I need to ground them all for it to use the lower 2K of address space?

with a few jumpers I managed to put all 8 ROMS of both BASIC 1 and 2 into one and select the version with a jumper.

Hi Mike,

Is there a post somewhere explaining how to do this? I am interested in getting all the basic 1 roms into 1 eprom, that would save me using all these adapters. Is that possible? If so do I just get a 16k eprom and put all the roms on that?

Is it the old version or the new one? Is the '138 a DIP or SMT version?

I assume its the new version as I've only recently got them.

Thanks!

Dan

 

[MikeS]

Hi Mike,

Is there a post somewhere explaining how to do this? I am interested in getting all the basic 1 roms into 1 eprom, that would save me using all these adapters. Is that possible? If so do I just get a 16k eprom and put all the roms on that?
Dan

It was something I tried a year or two ago when I first got some of those adapters just to see if it worked; it did, but it was pretty messy as it involves running a half dozen or so jumpers to the board and a couple of diodes & resistors (mainly to exclude the E800 I/O area), so I wouldn't recommend it, but I'll see what I can still find about it next time I'm rooting around in my PET stuff.

Give Jim the business and just get a set of adapters; I'd have to look at the 2001-8 schematic, but I *think* you can get by with only four adapters with 4K in C, D and F, instead of 7 x 2KB.

What you could also do is put both versions of BASIC into each of the ROMs and connect the select wires to a common switch or jumper to select one or the other.

 

[dave_m]

Thanks for the advice, I duplicated the 2k across the 8k space and it worked. On the board are holes A11-A15, so I need to ground them all for it to use the lower 2K of address space?

Yes, you want to point the EPROM to the lower 2K. I checked the schematic and the upper address lines are not hooked up in the character generator on the old PET so it is safe to ground the lines on the adapter. It will not short the actual upper address lines on the PET.

 

[dansretropod]

Yes, you want to point the EPROM to the lower 2K. I checked the schematic and the upper address lines are not hooked up in the character generator on the old PET so it is safe to ground the lines on the adapter. It will not short the actual upper address lines on the PET.

Cool that's great thanks for letting me know. I need to check the schematic then, I need to replace some of the other roms with these adapters too , don't want to short anything out:shocked:

 

[MikeS]

Yes, you want to point the EPROM to the lower 2K. I checked the schematic and the upper address lines are not hooked up in the character generator on the old PET so it is safe to ground the lines on the adapter. It will not short the actual upper address lines on the PET.

I think you're confusing the upper address lines on the adapter with those on the PET. There's no connection between the two, or risk of shorting anything; the pads on the adapter are just the upper address lines of the EPROM which can be as large as a '512 connected to a '138 decoder, and you'd normally jumper them to ground according to where your 2K or 4K image is located within the EPROM or connect them to a switch or jumper to select different areas, and left unconnected they'd presumably select the highest segment of whatever EPROM is plugged in.

Since A11 goes to all sockets you can put a 2732 (or larger) in either the high or the low C, D and F ROM sockets and only use 4 ROMs and adapters instead of 7. I don't recall offhand whether Jim's had that problem, but some adapters are too wide to fit into adjacent sockets and you might have to use 4K ROMs leaving 3 sockets empty.

 

[brain]

If you have any issues, email me (you can post here as well, but forums are the last thing I check after after filling orders and checking email

Jim