IBM 1 Series - System-Related Characteristics

Write Control
System-Related Characteristics
Power Failure
Error Recovery
A Write command has the following format:
Bits 0-3 Bits 4—7
0101 000X
Bit 7 of a Write command controls the ‘write control’ output. If a Write
command is issued with bit 7=1, the ‘write control’ output closes and
remains closed until either (1) a Write command is issued with bit 7=0, or
(2) the attachment is reset.
If a Write command is issued with bit 7=0, the ‘write control’ output
opens and remains open until a Write command is issued with bit 7=1.
Any system reset or device reset causes the ‘write control’ output to open
and remain open until a Write command is issued with bit 7=1.
A Write command can change the state of the ‘write control’ output only
if the IO condition code response to the command is condition code 7
(command accepted).
A Write command cannot change the state of the ‘write control’ output if
the IO condition code response to the command is condition code O
(device not attached), 1 (write busy), 3 (command reject), or 5 (interface
data check). The teletypewriter attachment does not use IO condition code
2, 4, or 6.
Write Control Timing. The ‘write control’ output can change state only
during the first 0.2 microsecond of the start bit of a transmit operation. It
is opened by a system reset or device reset.
Any character that is in the process of being either transmitted or received
during a power failure is either lost or garbled.
‘Power-on reset’ is generated when the system is powered back up. This
signal resets all controls and registers in the teletypewriter adapter except
for the receive serializer/deserializer register. This register is set to all 1’s.
(This is equivalent to the ASCII ‘“‘rub out’ character.)
There is no checking of any kind between the teletypewriter adapter and
the user’s device.
Teletypewriter Adapter Feature 4-21