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executed sequentially ('read result type' first), and should be executed only in response to an interrupt request from
the Diskette Channel; execution at other times could produce erroneous result data.
The use and format of each of the six channel commands is described below:
WRITE MEMORY ADDRESS LOWER (OUTPUT)
-
-
.
This channel command outputs the low order byte of the 16-bit memory address that points to byte 1 ('channel word')
of the IOPB.
,.. _
_
_.
System address bus:
BASE + 1
\
System data bus:
Eight least significant bits of the 16-bit memory address that points to the
first IOPB.
WRITE MEMORY ADDRESS UPPER AND START THE DISKETTE OPERATION (OUTPUT)
This channel command outputs the high order byte of the 16-bit memory address that points to byte 1 of the IOPB.
This command also causes the Diskette Channel to begin executing the diskette operation specified in byte 2 (instruction
byte) of the addressed IOPB.
System address bus:
BASE + 2
System data bus:
Eight most significant bits of the 16-bit memory address
.
. ,
RESET DISKETTE SYSTEM (OUTPUT)
This output channel command causes all control logic in the Diskette Channel to be reset in an initialized state. If
this command is issued while a 'write data' diskette operation is in progress, the data in the sector currently being
written will be garbled. This command is intended to clear a 'hang up' in the Diskette Channel.
System address bus:
,
BASE + 7
System data bus:
Not used.
$• +
READ SUBSYSTEM STATUS (INPUT)
This input channel command causes the Diskette Channel to return.
bit 0 - ready status of drive 0
bit 1 — ready status of drive 1
bit 2 — state of the channel's interrupt flip-flop
bit 3 — controller presence indicator
bit 4 — double density controller presence indicator
bit 5 — ready status of drive 2
bit 6 — ready status of drive 3
2-3
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