Apple Lisa - Page 47

Confidential
Lisa Hardware Reference Manual
The
15 hard disk interface signal lines are controlled by a 6522. The
relevant 6522 lines are:
6522
line
disk
interface
PAO - PA7
Peripheral A Port
DDO - DD7 Disk Data
CAl Control line 1 A PSTRB/
Processor
Strobe
CA2 Control line 2 A latch CAl
PB2
Peripheral B Port
2 DEN
Disk Enable
PB3
Peripheral B Port 3
RW
Read/Write
PB4
Peripheral B Port
4
CMD Command
PBS Peripheral B Port
5 OCD Open Cable Detect
PB6 Peripheral B Port
6 PARIT'l./
Parity error
PB7 Peripheral B Port
7
BRC
Baud Rate Control
PB7 on the Keyboard 6522 CRES/ Controller Reset
CB2 Control line 2 B BSY Busy
PAD - PA7 The slow data bus. These eight bits are buffered with
7-Jul-8l
an LS245 to produce the eight Disk Data lines (000 - 007).
They are also used to provide data to the contrast
control latch.
CAl CAl generates the PSTRB/ signal. If CAl is in pulse
handshake mode, and the DEN bit is low, the CAl line
produces the proper pulse to transfer data to or from
the disk with each read or write to the Peripheral A Port.
CA2 CAl is fed directly to CA2 to allow latch mode to be
used on the Peripheral A Port while data is being read
from the disk.
PBO - PB7
+---+---- I .-- I .---+--- I ----+-----+
I BRC I RDP ( OCD ( CMD
RW (DEN ( ( I
Lisa
-1------1--------+----+------+-_._--+----+-----+-----+
PB7 PB6 PBS PB4 PB3 PB2 PBI PBO
Synertek
·PBO - PBI
DEN
RW
Unused.
Disk Enable. DEN enables the buffers which
drive the disk interface lines. When DEN
is low, the buffers are enabled. When DEN
is high, they are disabled.
RW controls the disk Read/Write line, and sets
the data direction on the LS245 buffer for the
Disk Data lines. When RW is high, the DO lines
are enabled to read from the disk. When RW is
low, the DO lines write to the disk.
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