IBM Personal System/2 65 SX User Manual

System-Control Port B (Hex 0061)
Bit definitions for the write and read functions of this port are shown
in the following tables.
Bit Function
7 Reset Timer 0 Output Latch (IRQO)
6-4 Reserved
3 Enable Channel Check
2
1
0
Enable Parity Check
Speaker Data Enable
Timer 2 Gate to Speaker
Figure 3-22. System-Control Port B (Write)
Function
Parity Check
Channel Check
Timer 2 Output
Toggles with Each Refresh Request
Enable Channel Check
Enable Parity Check
Speaker Data Enable
Timer 2 Gate to Speaker
OeaNnNWAAADN
Figure 3-23. System-Control Port B (Read)
Bit7 When set to 1 during a write operation, this bit resets IRQO.
When read as a 1, this bit indicates a parity check has
occurred.
Bit 6 When read as a 1, this bit indicates a channel check has
occurred,
Bit5 When read, this bit indicates the condition of the timer 2
‘output’ signal.
Bit4 When read, this bit toggles for each refresh request.
BIt3 When set to 0, this bit enables channel check. This bit is
set to 1 during a power-on reset.
Bit2 When set to 0, this bit enables parity check. This bit is set
to 1 during a power-on reset.
Bit1 When set to 1, this bit enables speaker data.
Bit 0 When set to 1, this bit enables the timer 2 gate.
Model 65 System Board — October 1990 3-23

IBM Personal System/2 65 SX Specifications

General

Brand	IBM
Model	Personal System/2 65 SX
Category	Desktop
Language	English