ZiLOG System 8000 Hardware Reference Manual page 124

HRM
2ilog
DISPATCH TABLE
15 14 13 12 11 10
9
8 6
5
4 3 2
HRM
1 0
00 PSO
02 PS1
04
PS2
06 PS3
08 PHO
OA PLO
OC PH1
OE PL1
10 PH2
12 PL2
14
PH3
16
PL3
packet status - drive 0
packet status - drive
1
packet status - drive 2
packet status - drive 3
packet address msh - drive
0
packet address Ish - drive
0
packet address msh - drive
1
packet address Ish - drive 1
packet address fish - drive
2
packet address Ish - drive 2
packet address msh - drive 3
packet address Ish - drive
3
DT:PS VALUES: 0
=
IDLE (set by host)
1
=
GO (set by host)
2
=
BUSY (set by SMDC)
4
=
DONE (set by SMDC)
When an operation is to be initiated, the control informa-
tion must be loaded into the appropriate packet and the
.corresponding dispatch table status word (DT:PS) set to GO.
A command word is then issued with CR:WK (wakeup) and
optionally CR:EI (enable interrupt). Wheh the controller is
idle, it interrogates the wakeup bit, sees it turned on,
turns it off, and reads the dispatch table. Any dispatch
table entries with packet status
=
GO cause the correspond-
ing packets to be read into the SMDC's internal packet
tables and DT:PS to be set to BUSY.
Internally, seeks are initiated on any drive with an active
packet requiring a seek. When a seek is complete, or if no
seek is required (e.g. select command), the command is per-
formed and the packet in host memory updated with status,
the dispatch table status set to DONE and IP posted. The
host may be scanning SR:IP or waiting for an interrupt with
CR:EI set.
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