Test Device Instruction - RCA 70/46 Reference Manual

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Block 9
(Cont'd)
Test Device
Instruction
Input/Output Operation
2. The standard device byte is not stored if the condition codes are
0, 2, 3.
3. If an interrupt pending (termination or external device request)
condition exists on a specified selector channel, the condition code
is set to zero.
4. The channel and device are terminated at the next data service
request (see Servicing a Data Transfer).
5. The Channel Address Word ( CAW), Channel Block Address (CBA),
and Channel Command Word (CCW) are not used by this instruction.
6. If execution of this instruction causes the standard device byte to
be stored in the multiplexor channel registers, the program must
inhibit interrupts from the multiplexor channel until the standard
device byte has been analyzed or moved from the channel registers.
If interrupts are permitted and one occurs, the standard device
byte is destroyed .
The status of an input/output device can be tested by executing a Test
Device instruction. The Test Device instruction is a privileged operation
and can be executed only if the mode bit (bit position 15 of the Interrupt
Status register for the current state) is set to 0. This instruction is exe-
cuted in the normal mode. Continuation of program execution is delayed
until the instruction is terminated.
Both the channel number and the device number must be specified in
the instruction. Because the Channel Address Word is not referred to by
the Test Device instruction, the Channel Address Word, Channel Block
Address, and a Channel Command Word are not required.
Upon execution of a Test Device instruction, the following events occur
(see figure 7).
Block
1
If the privileged mode bit (bit position 15 of the Interrupt Status
register) for the current state is not set to 0, the privileged operation bit
is set in the Interrupt Flag register and an interrupt occurs, if permitted.
Block
2
If the specified channel is a selector channel that is not available on
the system, the condition code is set to 3, the Test Device instruction is
terminated and program control is transferred to the next instruction.
Block 3
If the specified channel is a selector channel that is busy or has on
interrupt pending (termination or external device request) ; or if the speci-
fied channel is the multiplexor that is operating in the burst mode, the
condition code is set to 2, the Test Device instruction is terminated and
program control is transferred to the next instruction.
Block 4.
The channel status byte and the standard device byte for the specified
channel are reset to zeros in the appropriate channel registers.
Block
5
The device address as specified in the Test Device instruction is sent
to all trunks on the addressed channel.
56

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