Epson PC AX Technical Manual page 205

REV.A DIAGRAMS AND REFERENCE MATERIALS
e. "OOh" is written to the shutdown byte, then this operation is
terminated.
3) 27256 ROM Checksum Check
The 27256 ROM checksum check performs a check on the sum total
of all 27256 ROM data in byte units, then confirms whether or not
that sum equa1s "OOh". The program displays an error message
if
the
sum does notequal "OOh".
+-----------------------------------------------------------------+
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: Error code
=
102
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: 27256 ROM CHECKSUM ERROR :
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+-----------------------------------------------------------------+
4) 8254 Timer Counter Check
The 8254 Timer Counter check performs acheck of the setting
and reading operation of the counter register of the 8254 Timer
Counter.
Count "0" of the 8254 Timer Counter is 1atched and the count
va1ue is checked. Next, acheck is repeated1y performed to confirm
that all 16 bits have the va1ue of "1". The program displays an
error message if any bit of the count va1ue of "1" cannot be read.
+-----------------------------------------------------------------+
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: Error code
=
103 :
: 8254 TIMER COUNTER REGISTER ERROR
l
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+-----------------------------------------------------------------+
5) 8237 DMA Controller Check
The 8237 DMA Controller check performs a WRITE/READ check on
the eight registers (Port Nos. OOh to 07h) of the first 8237 DMA
Controller and on the eight registers (Port Nos. COh, C2h to CEh)
of the second 8237 DMA Controller.
The test data is used in the sequence of "OOOOh", "5555h",
"Oaaaah", and "Offffh". If an error is detected, the fo11owing
message will be disp1ayed:
+-----------------------------------------------------------------+
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: Error code
=
105
I
: 8237 DMA CONTROLLER REGISTER ERROR :
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+-----------------------------------------------------------------+
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