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DATA FLOW FUNCTIONAL COMPONENTS
Parity Check
This block is used in all modes of operation. It checks
for odd parity on the' data bus out' line. The parity bits
are generated in the system. If an odd parity exists, the
bytes are passed to the appropriate circuits. If an even
parity exists, the 'machine check' line to the system is
activated, and the remaining bytes coming in are
ignored. This block also checks the X and Y device
address lines. Only one X line and only one Y line must
be active. If any other condition exists, the 'machine
check' line is activated.
Address Decode
This block reads all address bytes coming to the adapter
for hex D. Hex D is the address byte for a diskette
drive. Any other address will be ignored. When an
address of hex D is decoded, the commands that follow
the address are passed to the appropriate circuits.
The hex D is converted to a binary number to activate
the X and Y device address lines.
Device Address Hex D= 11 01
~~
0011
0001
I
\
X Address \ 01010111
r-\0\F"""' T 11"""01"""01 Y Address
Line
0 1 2 3
0 1 2 3
Line
Diskette Control Card Controls
This block is used in all modes of operation. There are
several lines to this block that perform the tasks necessary
to read, write, and load the heads. These lines are as
follows:
+Write Data:
For each change of the write data signal, the
current switches in the read/write head. This process
records the data on the diskette surfaces. (See Logic 440.)
+Select Head 1:
When active, this line selects head 1.
(See Logic 440.)
IOn card PIN 4178065, this line is called '+current enabled'.
+Inner Tracks:
On a write operation, this line is used to
reduce the amount of recording current beyond the
middle cylinders. On a read operation, this line is used to
compensate for bit shifting beyond the middle cylinders.
+Write Gate:
Write gate activates the write circuits and
deactivates the read circuits for a write operation. (See
Logic 440.)
+Erase Gate:
Erase gate activates the erase circuits for a
write operation. (See Logic 440.)
+Inner Track Select:
This line is used with the inner tracks
line to further compensate for bit shifting beyond
cylinder 60 for MFM encoding. This line is not used on
a write operation.
+Erase Current Sensei:
When this line is active, the
erase circuits are working OK.
+File Data:
File data is a series of clock and data pulses
that represent the data read from the diskette surface.
Note:
On card Pn 4178065, this line is called '+ current
enabled'.
+Index:
This line indicates the beginning of a track. This
1.5 to 3.0 ms pulse occurs every 166.7 ms.
+Diskette 2 Sense:
When active, this line indicates that a
diskette 2 or 2D is being used. This line is not activated
by a diskette 1.
+Head Engage:
When active, this line loads the read/write
heads.
-Diskette Drive Sense:
This line is used by the adapter
card to sense if a second drive is installed.
+Access Lines 0 through 3:
Two of the four access pulses
move the read/write heads from one cylinder to the next
cylinder. Notice in the chart that the same pair of access
pulses are repeated every four cylinders.
Diskette Adpater Card
3-27
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