Table 2-1 Typical Header/Instruction Byte; Table 2-2 Command Header/Instruction Bytes - Wang DW/OS-20 Maintenance Manual

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Header/Instruction bytes, which precede all data transfers, have to be
detected and decoded for initiating the proper operation internally in the •
data link. A header code of 101 (consists of the MSB's D 7 and Ds) is
detected internally to set up the instruction bits (D 4 -D 0 ) as shown in
table 2-1.
Table 2-1
TYPICAL HEADER/INSTRUCTION BYTE
TIME 0
MSB*
LSB
BITS
1
2 J
4
5
6 7
8 9
10
11
START D7
D6 D5
D4 DJ D2
Dl DO PAR STOP
1
1
0 1
x
x x x
x x
0
(SYNC
BIT)*
Each Command Header/Instruction byte is shown in the table 2-2 below. •
Table 2-2
COMMAND HEADER/INSTRUCTION BYTES
TIME 0
HEADER
INSTRUCTION
D7 D6
DS D4 DJ
D2 Dl DO PAR COMMAND
1
0 1
1 0
0 0
1
0 STATUS
1
0
1
0
1
0 0 0 1
RESTART
1
0
1
0 0
1
0
0
1
256-BYTE RD
1 0 1
0 0
1
0
1
0
256-BYTE WR
1
0
1
0
0 0
1
0
1
1-BYTE READ
1
0
1
0
0 0 1
1
0 1-BYTE WRITE
•
The Header/Instruction bytes in table 2-2 are decoded in the data link
portion of the Siblink and
proc~ssed
as described in the following paragraphs.
2-6