pjh
Experienced Member
After acquiring a 3rd CCS 2422 FDC and checking it out, I was able to boot the CCS CP/M disk
that I have. I have two other 2422s that I couldn't get to work after chip testing
everything on those boards except the PROMS. PROMS have been a gray area for me but I
figured that these must be the problem on the first two boards. I listed the PROM chips on
each of the boards and this is what I have:
U22 U23
--------- ---------
1st 2422 IM5623CPE IM5623CPE
2nd 2422 MB7057 IM5623CPE
3rd 2422 IM5623CPE TB24S10N
Next I wanted to test each of these chips in the other boards. The 3rd board still worked
with each of the U23s , so I have three good U23 chips. The 3rd board fails with each of
the other U22 chips. The 1st and 2nd boards work with the 3rd board's U22 chip.
I then decided to delve a little deeper into this gray area of PROMs and bread-boarded a
little debounced single-step circuit to dump the contents of the chips out to a TIL311
hex display.
The U23 chips have 'F's in all of the memory locations except these:
0 1 2 3 4 5 6 7 8 9 A B C D E F
---+---------------------------------------------------------------
F0 D D D D D D C C F F F F F F F 7
The working U22 chip has this code:
0 1 2 3 4 5 6 7 8 9 A B C D E F
---+---------------------------------------------------------------
00 F F F F D F F F F F F F F F F F
10 F F F F F F F F F F F F F F F F
20 F F F F F F F F F F F F F F F F
30 B B B B 5 F F F F F F F F F F F
40 E F F F F F F F F F F F F F F F
Not the 'D' in location 04, the 'B's in locations 30-33, the '5' in location 34 and
the 'E' in location 40
Every other memory location in the U22 from 50 to FF has 'F's in it.
This brings up the questions that I have about the 1st board's IM5623CPE and the 2nd board's
MB7057.
Both the 1st board and the 3rd board have IM5623CPEs as the U22 chips. In fact, both '5623
chips have the exact same programmed contents. But the 1st board's '5623 fails to work and
the 3rd board's '5623 works. Is there a characteristic of Bipolar Proms where a chip could
be coded correctly, have the contents readable, but still fail?
The 2nd board's MB7057 is programmed with the correct data but in the wrong memory location,
so I haven't botherd to show its contents. However, I have a question about it. The MB7057
is an Open-collector chip. The '5623s are Tri-state. In what searching I have done on
Bipolar Proms, I seem to recall a mention in another forum that in some circuits, using either
Tri-state or Open-collector Bipolar Proms wouldn't matter. If the MB7057 had been
programmed correctly, would it have worked or would it have to have been an MB7052
Tri-state chip?
that I have. I have two other 2422s that I couldn't get to work after chip testing
everything on those boards except the PROMS. PROMS have been a gray area for me but I
figured that these must be the problem on the first two boards. I listed the PROM chips on
each of the boards and this is what I have:
U22 U23
--------- ---------
1st 2422 IM5623CPE IM5623CPE
2nd 2422 MB7057 IM5623CPE
3rd 2422 IM5623CPE TB24S10N
Next I wanted to test each of these chips in the other boards. The 3rd board still worked
with each of the U23s , so I have three good U23 chips. The 3rd board fails with each of
the other U22 chips. The 1st and 2nd boards work with the 3rd board's U22 chip.
I then decided to delve a little deeper into this gray area of PROMs and bread-boarded a
little debounced single-step circuit to dump the contents of the chips out to a TIL311
hex display.
The U23 chips have 'F's in all of the memory locations except these:
0 1 2 3 4 5 6 7 8 9 A B C D E F
---+---------------------------------------------------------------
F0 D D D D D D C C F F F F F F F 7
The working U22 chip has this code:
0 1 2 3 4 5 6 7 8 9 A B C D E F
---+---------------------------------------------------------------
00 F F F F D F F F F F F F F F F F
10 F F F F F F F F F F F F F F F F
20 F F F F F F F F F F F F F F F F
30 B B B B 5 F F F F F F F F F F F
40 E F F F F F F F F F F F F F F F
Not the 'D' in location 04, the 'B's in locations 30-33, the '5' in location 34 and
the 'E' in location 40
Every other memory location in the U22 from 50 to FF has 'F's in it.
This brings up the questions that I have about the 1st board's IM5623CPE and the 2nd board's
MB7057.
Both the 1st board and the 3rd board have IM5623CPEs as the U22 chips. In fact, both '5623
chips have the exact same programmed contents. But the 1st board's '5623 fails to work and
the 3rd board's '5623 works. Is there a characteristic of Bipolar Proms where a chip could
be coded correctly, have the contents readable, but still fail?
The 2nd board's MB7057 is programmed with the correct data but in the wrong memory location,
so I haven't botherd to show its contents. However, I have a question about it. The MB7057
is an Open-collector chip. The '5623s are Tri-state. In what searching I have done on
Bipolar Proms, I seem to recall a mention in another forum that in some circuits, using either
Tri-state or Open-collector Bipolar Proms wouldn't matter. If the MB7057 had been
programmed correctly, would it have worked or would it have to have been an MB7052
Tri-state chip?