MC68HC901 Datasheet, PDF (27/73 Pages) Motorola, Inc – Multi-Function Peripheral

Interrupt Structure
4.3 INTERRUPT CONTROL REGISTERS
MFP interrupt processing is managed by the enable registers A and B, interrupt pending
registers A and B, and interrupt mask registers A and B. These registers allow the
programmer to enable or disable individual interrupt channels, mask individual interrupt
channels, and access pending interrupt status information. In-service registers A and B
allow interrupts to be nested as described in Section 4.4 Nesting MFP Interrupts. The
interrupt control registers are shown in the following paragraphs.
4.3.1 Interrupt Enable Registers (IERA, IERB)
The interrupt channels are individually enabled or disabled by writing a one or a zero,
respectively, to the appropriate bit of interrupt enable register A or B (IERA or IERB). The
processor may read these registers at any time.
When a channel is enabled, interrupts received on the channel will be recognized by the
MFP, and IRQ will be asserted to the processor indicating that interrupt service is required.
On the other hand, a disabled channel is completely inactive; interrupts received on the
channel are ignored by the MFP.
Writing a zero to a bit of interrupt enable register A or B will cause the corresponding bit of
the interrupt pending register to be cleared. This will terminate all interrupt service requests
for the channel and also negate IRQ unless interrupts are pending from other sources.
Disabling a channel, however, does not affect the corresponding bit in interrupt in-service
registers A or B. So, if the MFP is in the software end-of-interrupt mode (refer to Section
4.4.3 Software End-Of-Interrupt Mode) and an interrupt is in service when a channel is
disabled, the in-service bit of that channel will remain set until cleared by software.
IERA REGISTER
BIT
7
FIELD
GPIP7
RESET
0
ADDR
6
GPIP6
0
5
TIMER A
0
4
3
RCV
BUFFER
FULL
RCV
ERROR
0
0
$07
2
XMIT
BUFFER
EMPTY
0
1
XMIT
ERROR
0
0
TIMER B
0
GPIP7-GPIP6 — General Purpose Interrupt Enable
1 = Enable.
0 = Disable.
Timer A — Timer A Interrupt Enable
1 = Enable.
0 = Disable.
Receiver Buffer Full — Receiver Buffer Full Interrupt Enable
1 = Enable.
0 = Disable.
4-4
MC68HC901 USER’S MANUAL
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