IBM 1 Series - Functional Subsets of the Signal Lines

Functional Subsets of the Signai Lines
Basic Subset
2-4 GA34-0033
The I/O channel signal lines can have subsets, depending on the level of
function required by the I/O attachment. In order of increasing level of
function, these subsets are: |
e Basic subset
e Interrupt subset
e Cycle-steal/IPL subset
Attachment to a subset is a prerequisite for attachment to the next higher
level subset.
The basic subset consists of the buses and tags to support functions
initiated by the processor; for example, direct program control (DPC)
commands. This includes the data transfers associated with the DPC
command itself. The basic subset supports DPC devices that do not
interrupt. I/O signal lines in the basic subset are shown in Figure 2-3.
Service group signal lines
Signal Number
name Direction of lines
Address bus bits 0-15 (Note 1) ——=——=——> | ()
Address bus bit 16 ———— |
Data bus (Note 2) ————np 18
Address gate ———— |
Address gate return —— |
Condition code in bus —————— 3
Data strobe ——————s |
Halt or MCHK ae
System reset —————————p |
Power on reset ———esp |
Poll group signal lines
Poll (Note 3) —_—————> |
Poll prime (Note 3) ——_—_——————p |
Poll propagate (Note 3) en |
Notes:
1. Address bus bits 0-15 need only be received in this subset.
2. Bidirectional data bus capability is assumed for this subset; however, if the
direction of data flow within a device is fixed (specifically, a read-only device
attachment with no write or interrupt capability), the device need not implement
bidirectional data drivers and receivers. In this case, the device must reject all
commands requiring a transfer in other than the direction implemented by the
device. For the interrupt subset (described in “Interrupt Subset” in this chapter),
the device must implement bidirectional data bus drivers and receivers.
3. ‘Poll and "poll prime’ need only be received, logically ANDed, and redriven on
the ‘poll propagate’ line to maintain continuity of the serial poll mechanism. Any
card installed on the channel, even though it does not operate on the channel,
must propagate ‘poll’ and ‘poll prime.’
Figure 2-3. Basic subset