This might be slightly off topic but it does involve operation on a real
1620.
I have the coding for a transition program IBM wrote to help 1620 users move
to 360/370 computers. I have a good portion of the code working but I've
run into a
snag testing out the Disk Utility Program.
A sequence of
>Is the RM and possibly Group Mark valid in a P or Q address and if so, what
>would be the
>value in the address? Could the RM be a 0 and the GM () be a 5 using
>modulo 10.
My guess would be that an RM (or any other invalid digit) does nothing
special when entered into the MARS, b
There's nothing conditional about the user documentation. The 1965
reference manual says, "MARS (Memory Address Register Storage) Check
Light. This light is turned on when a digit in MARS has a parity error
or an invalid address. These errors halt the machine immediately."
Now the key question
> On Dec 23, 2015, at 4:30 PM, Bob Supnik wrote:
>
> There's nothing conditional about the user documentation. The 1965 reference
> manual says, "MARS (Memory Address Register Storage) Check Light. This light
> is turned on when a digit in MARS has a parity error or an invalid address.
> Thes
It's worse than that. The detailed logic is shown on 227-5631-0 pp
188ff. The decode chart for each decode switch (DSW) is:
DSW 0
DSW 10001
DSW 20010
DSW 3X011
DSW 4X100
DSW 5X101
DSW 6X110
DSW 7X111
DSW 81XX0
DSW 9
>So either no core is selected or multiple cores are selected.
> Now what happens?
The unanswered question here is "What are the conditions for setting MAR
CHECK"?
If an invalid digit in the MAR sets MAR CHECK, then the decoding is
irrelevant.
Bob
P.S. Merry Christmas, guys!
__
> On Dec 25, 2015, at 2:21 AM, Bob Supnik wrote:
>
> It's worse than that. The detailed logic is shown on 227-5631-0 pp 188ff. The
> decode chart for each decode switch (DSW) is:
>
> DSW 0
> DSW 10001
> DSW 20010
> DSW 3X011
> DSW 4X100
> DSW 5
Bob A is right. I found the MAR checking logic on pp 292-3 of 227-5631-0.
For the low four digits of MAR, there are two circuits: a C-bit checker
and an invalid digit checker.
C-bit checker is: (b4 xor b2) xor (b1 xor b8) xor C
invalid digit checker is: (b4 or b2) and b8 - which picks up 1010
> an invalid digit in MAR generates MAR ERROR, lights the MAR
>CHK LAMP, and stops the system.
I thought that might be the case. Thanks for researching it.
BTW, I was wrong about the check stop switch bypassing the MAR CHECK - I
found several references in the manual that make it clear tha
> On Dec 25, 2015, at 2:21 AM, Bob Supnik wrote:
>
> ...
> So either no core is selected or multiple cores are selected. Now what
> happens? I suspect it's something bad.
FWIW: given how core works, if more than one core select line is active, the
read cycle will see the OR of the two selecte
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