Adding 2716 EPROMs to 502 board

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nama
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Adding 2716 EPROMs to 502 board

Post by nama »

I wanted to document the process, for anyone who is interested, of replacing or adding 2716 EPROMs to the 502 board. For those who followed the thread on the fix of my recently acquired, and very hacked up 502 board, will remember that it did not have any BASIC ROMs installed. I wanted to find a simple and elegant solution to installing 2716 EPROMs as a replacement.

The 502 board comes standard with 2316 ROMs. 2316 ROMs come in a variety of different types. The Apple II, Commodore 2001, and old vIdeo games, to name a few, all use 2316's. However, I believe that companies could order 2316's from the manufacturer in different configurations, with the differences being wether the chip select lines were active high or low (I could be a little confused about the exact details). Unfortunately the 2716 EPROMs chip selects are opposite to the 2316's used in the OSI, otherwise the pinouts are basically compatible.
There are two Pins (18 and 20) on each EPROM that will need to be dealt with, and how you deal with them differs on wether you are installing the Monitor ROM or the four BASIC ROMs.
I will discuss each one separately...

-MONITOR ROM-
Fortunately replacing the Monitor ROM with a 2716 EPROM is easy, and OSI has provided simple onboard jumpers to do this. (Due to the 3 image upload limit please take a look at the next post in the thread for 502 schematics highlighting the jumper area). Once these two jumpers are changed you will be able to simply drop in a 2716 EPROM. Easy!

-THE 4 BASIC ROMs-
This is where things get a little more difficult….but not too much.
OSI has not made it easy to replace the BASIC ROMs with EPROMs, with no easy jumpers like those for the Monitor ROM.
Again pins 18 and 21 will need to be dealt with. I will explain each pin individually.

Pin 18:
OSI seems to have dealt with pins 18 and 20 differently between BASIC ROM 4 and BASIC ROMs 1,2, and 3. Looking at the schematic it seems that BASIC 4 was able to be replaced with a 2664 (see following post for schematic). Not sure what a 2664 is, but this means that first we have to find a way to tie pins 18 on BASIC ROMs 1, 2, 3, and 4 together, and then connect this all to GND. Here's how:

On the parts side there is a single trace under U8 (BASIC ROM 1) which connects pins 18 and 21, you will need to cut this, but be aware that it's a little hard to get too as it is under the right side of the socket. The schematic actually shows these pins to be connected on each ROM but this is not the case, and only this one line needs to be cut.
U8 Cut trace.JPG
U8 Cut trace.JPG (240.71 KiB) Viewed 7838 times
There is a jumper area above and to the left of U9 (BASIC ROM 4). Cut this.
Jumper area cut trace.JPG
Jumper area cut trace.JPG (119.52 KiB) Viewed 7838 times
On the solder side you will need to run a small jumper wire between U8 pin 18, and U9 pin 18. This ties pin 18 of all 4 BASIC ROMs together.
you will also see the solder side of the jumper area where you previously cut the trace. Use another short jumper wire to jumper between here and the GND line.
Jumpers.JPG
Jumpers.JPG (130.82 KiB) Viewed 7833 times
This takes care of pins 18 for all the 4 ROMs. They will now all be connected nicely to GND.

Pin 20:
The next part is a little more tricky. Pins 20 from the ROMs pass through a 7404 inverter at U17 which lies between the ROMs and a 74139 at U16. As I previously mentioned the 2716 does not need the CS signal inverted, therefore the 7404 is not needed. I decided the simplest and cleanest way was to remove the 7404 and put a socket in its place. Then I used small wires to jumper the socket. This way if I ever need to put the 7404 back in, there is a socket ready and waiting for it. The socket is jumpered in the following way:

3--4
5--6
8--9
10--11.

(see following posts for an image of the socket and jumpers)

That's all. The board should now be ready for 2716 EPROMs. I used the SYN600 Monitor ROM and BASIC ROM images found here (http://osiweb.org/software.html) to program my EPROMs. I also used the fixed BASIC 3 ROM image, as it resolves some garbage collector issues that the original BASIC 3 ROM had.

I have been possibly a little verbose in my instructions, but the process is actually very simple.

Have fun.

Philip
Last edited by nama on Sun Nov 25, 2012 10:51 am, edited 17 times in total.

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
nama
Posts: 357
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: Adding 2716 EPROMs to 502 board

Post by nama »

Schematic showing the jumper location to change to a 2716 Monitor ROM.
Schematic showing the jumper location to change to a 2716 Monitor ROM.
Monitor ROM.jpg (190.65 KiB) Viewed 7837 times
Image showing the jumper location to change to a 2716 Monitor ROM.
Image showing the jumper location to change to a 2716 Monitor ROM.
502 board layout.jpg (210.24 KiB) Viewed 7837 times
Schematic showing the 4 BASIC ROMs
Schematic showing the 4 BASIC ROMs
BASIC ROMs.jpg (104.65 KiB) Viewed 7837 times

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
nama
Posts: 357
Joined: Wed Mar 30, 2011 9:44 am
Location: New Zealand
Contact:

Re: Adding 2716 EPROMs to 502 board

Post by nama »

Image showing U17 7404 replaced with socket and then jumpered
Image showing U17 7404 replaced with socket and then jumpered
U17 Jumpers.JPG (111.1 KiB) Viewed 7837 times

2P (1mhz 32k) - 502 + 8k + CEGMON + garbage collector fix BASIC, D&N MEM-CM9 + 24k, 540 (mono) [SOLD]
4PMF (2mhz 24k) - 505, 540, 527, D13 + 5.25" + Gotek
Superboard RevD - CEGMON + 610 board 24k + D13
Spares - 3 x 527, 1 x 505, Backplane
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