IBM 3745 Series, Hardware Maintenance Reference

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Halt (HLT): The CCU activates the 'halt' line to indicate to the selected adapter
that the CCU has detected an error condition associated with the current operation.
The CCU will activate the 'halt' line after 'TA', 'CSGH', or 'CSGL' has been deacti-
vated. The CCU will deactivate the 'halt' line when it deactivates the 'I/O' line. The
selected adapter will terminate the current operation and set a check bit active in its
status register.
Out (R/W): The CCU activates the 'out' line, while the 'I/O' line is active, to indicate
that the direction of information on the data bus is outbound from the CCU. The
CCU deactivates the 'Out' line to indicate that the direction of information on the
data bus is inbound to the CCU.
Valid Byte (VB): A selected adapter will activate the 'valid byte' line during an AIO
operation to indicate a byte transfer instead of a halfword transfer. The valid byte
of information will be data bus byte 1.
Valid Halfword (VH): In some places the term 'valid' is used in place of 'valid
halfword'. A selected adapter will activate the 'valid halfword' line in response to
the activation of the 'TA', 'TD', 'CSGH', or 'CSGL' line from the CCU.
'Valid halfword' line active indicates that the adapter has either placed information
on the data bus or has received information from the data bus. It also indicates
that the CCU may deactivate its control line.
All adapters will activate 'valid halfword' when the CCU deactivates the 'I/O' line,
and deactivate 'valid halfword' when the CCU activates the 'I/O' line.
The CCU will proceed with an IO operation after all adapters have deactivated
'valid halfword'. A selected adapter will activate the 'end of chain' line instead of
'valid halfword' for the last halfword transfer of an AIO operation.
End of Chain (EOC) 'End of chain' active indicates that the AIO operation should
be concluded and that the adapter has either placed information on the data bus or
has received information from the data bus.
Modifier (M): A selected adapter will activate the 'modifier' line with 'valid byte' line
for the last byte transfer of a AIO operation.
'Modifier' line active at this time indicates that the AIO operation should be con-
cluded.
Parity Valid (PV): A selected adapter will activate 'parity valid' to indicate to the
CCU that it wishes to have parity checking of data inbound to the CCU.
If 'parity valid' is active and bad parity is detected by the CCU, the CCU will acti-
vate the 'halt' line.
If 'parity valid' is deactivated and bad parity is detected by the CCU, the parity is
corrected, the data is stored, and a status bit is set.
CA IPL Detect (CAIPL): A CA adapter will activate this line when it detects a
"WRITE IPL" command on the host interface. When the CCU receives this signal it
will raise a Level 1 interrupt to MOSS.
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IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference