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7. COMMUNICATION WITH PROGRAMMABLE CONTROLLER CPU
/ M E L s E c - A
(3) Bitlword specification
(a) When a system subroutine has been called with "bit" process-
ing specified, one byte of AD51 memory is used per bit. This
is illustrated below, the least significant bit indicates the state
of the specified b i t device for both reading and writing.
Data to be read
87 B 6 8 5 8 4 B 3 8 2 B l BO
All turn to
"0".
1 : O N
Data to be written
(b) When a system subroutine has been called with "word"
specified, and bit devices are t o be processed (i.e. in batches
of 16 devices) then one word of AD51 memory is used per
16 bits. This is illustrated below. The head device number
is X10 and state of this device is indicated by the least sig-
nificant bit. The states of the next 15 bits are stored in
consecutive bits from Bit B1 t o Bit 815.
B15 814 813 812 B l l B10 8 9
B 8
87
B6 B5 8 4 8 3
8 2
B1
BO
X12
X I 8
X1F
X I 1
X10
XlE
X I 0
X I 7
X1C
X16
X1B
X I 5
X1A
X I 4
X I 9
X I 3
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