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Theory of Operation
7942 and 7946
MNEMONIC
DATAO-H
thru
DATA7-H
DAV-L
DIOI-L
thru
DI08-L
DIR-L
DRIN-L/
DROUT-L
3-24
Table 3-1. List of Mnemonics (Continued)
SIGNAL
Read/Write
Data Bus, Bits 0
thru 7
Data Valid
HP-IB Data I/O
Bus, Bits I thru
8
Direction
Da ta Request
In/ Data
Request Out
SOURCE
AS/A2
~III
AS
m
AS
m
A2
III
A2
III
DESCRIPTION
DC-IB bidirectional 8-bit bus used to
pass read/write data between the
HDC and a selected DDC or vice ver-
sa.
Connected
between
HDC
PCA-AS
m
and DDC PCA-A2
III
via cable W2.
HP- IB handshake line used to indi-
cate availability and validity of in-
formation on Data I/O Bus DIOI-L
through DI08-L. DAV -L indicates to
a receiving device that data is a vail-
able.
HP-IB bidirectional data input/out-
put (I/O) bus used for the transfer of
data, commands, and other messages
between the host computer and the
HDC.
Transfer is bit parallel, byte
serial.
ST- S06
Interface
control
signal.
DIR-L defines the direction of mo-
tion of the read/write heads when
Step signal STEP - L is pulsed. An in-
active (high) DIR -L defines an "out"
direction and when STEP-L is pulsed,
the read/write heads move away
from the center of the disc. Converse-
ly, an active (low) DIR -L defines an
"in" direction and the read/write
heads move toward the center of the
disc. Output to disc drive assembly
Al _
via cable W3.
DC-IB tri -state DMA request lines
used
to
transfer
bytes
over
Read/Write
Data
Bus DATAO-H
through DATA 7-H. The "out" direc-
tion is defined as being from the
HDC
to
the
DDC.
A
DDC
is
programmed via Control/Status Data
Bus CSBO-H through CSB7-H to
drive a given request line. Output to
HDC PCA-AS
m
via cable W2.
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