IBM Series 1 - Page 29

Syste~ ~~2~i. This is an outbound tag received by all I/O
devices. The tag is singular in nature and meaning. When
the tag is detected, the I/O device must disable selection,
block poll propagation, and clear any status, states,
requests, registers, and interface control logic with the
following exceptions:
• Residual address
• Output sensor points
• Timer values
• Those registers not addressable by the software
During IPL sequences, one particular system reset has a
unique function. It viII be described in the "Operational
Characteristics" section to follow.
The receiver for this tag is always enabled.
Po,!!g,!:-Q!! !t~.§.g1. This is an outbound control line from the
power supply to all system components. This line is
activated on all power on/off sequences. While the line is
active, all system components are held in a system reset
state. The residual address, output sensor points~ and
timer values are also reset. The receiver for this line is
always enabled.
Each processor and I/O expansion unit on the I/O
channel has a self-contained unit power-on reset. These
paver-on resets are not electrically connected among units •
.R2!! GrQ.!!l! Ling Definition
Regu~§:!: In. l!.!!§. This is a 16-bit inbound bus used by an I/O
device to request an interrupt. Bits 0--15 of the request
in bus are used by I/O devices to request interrupts on
levels 0--15 respectively. Only levels 0--3 are used on
current processors. The level on which the device is to
interrupt corresponds to the encoded value in the level
field in the Prepare command.
~£le St~~lRequest In- This is an inbound tag used by a
cycle stealing device when an access to storage is required.
2-14 GA34-C033
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