MC68HC08AS32 Datasheet, PDF (86/280 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Table 4-5. BDLC Interrupt Sources
BSVR I3 I2 I1 I0
$00 0 0 0 0
$04 0 0 0 1
$08 0 0 1 0
$0C 0 0 1 1
$10 0 1 0 0
$14 0 1 0 1
$18 0 1 1 0
$1C 0 1 1 1
$20 1 0 0 0
Interrupt Source
No interrupts pending
Received EOF
Received IFR byte (RXIFR)
BDLC Rx data register full (RDRF)
BDLC Tx data register empty (TDRE)
Loss of arbitration
Cyclical redundancy check (CRC) error
Symbol invalid or out of range
Wakeup
Priority
0 (Lowest)
1
2
3
4
5
6
7
8 (Highest)
Upon receiving a BDLC interrupt, the user can read the value within the BSVR,
transferring it to the CPU’s index register. The value can then be used to index
into a jump table, with entries four bytes apart, to quickly enter the appropriate
service routine. For example:
Service
*
*
JMPTAB
*
LDX BSVR
JMP JMPTAB,X
JMP SERVE0
NOP
JMP SERVE1
NOP
JMP SERVE2
NOP
JMP SERVE8
END
Fetch State Vector Number
Enter service routine,
(must end in RTI)
Service condition #0
Service condition #1
Service condition #2
Service condition #8
NOTE:
The NOPs are used only to align the JMPs onto 4-byte boundaries so that the value
in the BSVR can be used intact. Each of the service routines must end with an RTI
instruction to guarantee correct continued operation of the device. Note also that
the first entry can be omitted since it corresponds to no interrupt occurring.
The service routines should clear all of the sources that are causing the pending
interrupts. Note that the clearing of a high priority interrupt may still leave a lower
priority interrupt pending, in which case bits I0, I1, and I2 of the BSVR will then
reflect the source of the remaining interrupt request.
If fewer states are used or if a different software approach is taken, the jump table
can be made smaller or omitted altogether.
Data Sheet
86
MC68HC08AS32 — Rev. 4.1
Freescale Semiconductor