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Command word 1 selects the . controller selector plug (P) into which the DSU is connected.
Once the DSU unit has been selected by the controller selector, the DSU controller goes into
the busy state and waits for the next two words from memory. The next two words are sent
to the DSU controller and indicates the operation to be performed (read or write), the file which
is to perform the operation, the number of frames to be transferred, and the starting address
in memory where information is to be sent or retrieved.
·
Bit positions 8 and 7 of word 1, and 18- 16 of word 2 cause the file to read (octal 12) or write
',octal 37). Bits 15- 13 of word 2 indicate the file which is to perform the read or write operation.
Bits 5 - 1 of word 2 indicates the number of records (0 - 16) which can be transferred. A "1"
in bit position 10 of command word 2 of a Read or Write sequence will cause power to be removed
from the positioning motor upon completion of that sequence. A "0" in bit position 10 of command
word 2 holds power to the positioning motor.
Bits 15 - 7 of word 3 transferred to the controller indicate the starting location in memory
of the read or write operation. The nine bits of the starting location address allow this address
in the controller to be stepped 1024 times or, in other words, to count the 1024 words of 16
records, the maximum which can be transferred by one instruction. Because bits 6 - 1 of word
3 are not used, the starting location address must be a multiple of 64. Bits 15 -
7
can address
memory capacities up to 32, 767 words.
BRANCH CONDITIONS
Single-access DSU branch conditions may be tested by looking at the B-register after a CSR
command. Bits 15, 16, 17, and 18 are on in the illustration below:
B-register
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
Controller Ready
Echo
Used for Dual Access
Controller
File 3 error
File 2 error
File 1 error
File 0 error
File error (any error)
Any error
Parity error
Input/output error
File 3 not ready
File 2 not ready
File 1 not ready
File 0 not ready
V-41
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