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4-31.
STATUS WORD. The status word results from various signals and flip-flops on the
SCMB. The conditions reported by the status word are reset each time I/O program execution is
initiated by an SIO instruction. Transfer related functions (eg, no compare) are reset at the beginning
of data transfers. Refer to figure 4-4 during the following description of the status word format.
4-32.
Bit 0 - SIO OK. This bit is a
~~1"
if the SCMB is not currently executing an I/O program
and the channel is inactive.
4-33.
4-34.
CPU.
Bit 1 -
RIO/WIO OK.
Always a
~~1".
Bit 2 - Interrupt Pending. This bit is a
~~1"
if the SCMB is attempting to interrupt the
4-35.
Bit 3 - Interrupt Active.
This bit is a
~~1"
if the SCMB interrupt circuitry is currently in
the active state.
4-36.
Bit 4 - Transfer Error. This bit is a
~~1"
if the channel has sent the XFER ERR (transfer
error) signal. Bit 4 is cleared by the next SIO instruction or I/O Reset.
4-37.
Bit 5 - SIO Enable. This bit is a
~~1"
if the channel is asserting the SIO ENABLE signal
(ie, channel inactive).
4-38.
Bit 6 - Device End. This bit is a
~~1"
if the SCMB has asserted the device end signal to the
channel. Bit 6 is cleared at the beginning of a new data transfer, by the next SIO instruction, or by an
I/O Reset.
",0 WID OK
I A L W A y S I O ~ K ,
I
I
INTERRUPT PENDING - - - - - - - - - '
INTERRUPT ACTIVE - - - - - - - '
TRANSFER ERROR
- - - - - - - - ~
SIO ENABLE FROM CHANNEL
- . . . J
DEVICE END
crn
---J
"XFER FF
IJ
O U T X F E R F F - - - - - - -
TERMINAL COUNT - - - - - - -
NO COMPARE - - - - - - - - - - - - - - - '
CLEAR INTERFACE - - - - - - - - - - - - '
'0"
7522-32
Figure 4-4. SCMB Status Word Format
4-12
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