IBM 1 Series - Halt or MCHK; System Reset; Power-On Reset; Diagnostic Mode and Diagnostic Mode Modifier

Halt or MCHK
System Reset
Power-On Reset
‘Halt or MCHK’ is a tag from the processor I/O channel to all I/O
devices. The tag means that a Halt I/O command has been issued by the
program or that a machine-check class interrupt has occurred. When this
tag is detected by an I/O device, the device must clear any status, states,
requests, interface control logic, and registers, with the following
exceptions:
e QOutput sensor points
e Timer values
e Those registers not addressable by the software
‘System reset’ is a tag to all attached I/O devices, and is singular in nature
and meaning. When ‘system reset’ is detected, an I/O device must reset
and clear any status, states, requests, registers, and interface control logic.
‘Power-on reset’ is an outbound control line from the power supply to all
system components. It is activated on all power on/off sequences. While
‘power-on reset’ is active, all system components are held in a system reset
state. Residual addresses, output sensor points, and timer values are also
reset. The receiver for this line is always enabled.
Diagnostic Mode and Diagnostic Mode Modifier
The ‘diagnostic mode’ line and the ‘diagnostic mode modifier’ line are
device-dependent. These lines can be used as programmable control lines
in conjunction with the Set Diagnostic Mode command (external diagnostic
mode).
Customer Direct Program Control (DPC) Adapter Feature 6-7