mc68hc912bc32 Freescale Semiconductor, Inc, mc68hc912bc32 Datasheet - Page 238

• Manufacturer Part Number: mc68hc912bc32
• Description: M68hc12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Byte Data Link Communications (BDLC)
238
Bits I0, I1, I2, and I3 are cleared by a read of the BSVR register except when the BDLC data register
needs servicing (RDRF, RXIFR, or TDRE conditions). RXIFR and RDRF can only be cleared by a read
of the BSVR register followed by a read of BDR. TDRE can either be cleared by a read of the BSVR
register followed by a write to the BDLC BDR register, or by setting the TEOD bit in BCR2. Clearing
an invalid symbol flag requires an EOF flag to be received before the BDLC can receive or transmit. If
ALOOP or DLOOP in BCR2 is set, the BDLC node is disengaged from the J1850 bus. Therefore, the
BDLC does not receive any data from the J1850 bus which normally generates BSVR flags.
Upon receiving a BDLC interrupt, the user may read the value within the BSVR, transferring it to the
CPU’s index register. The value can be used to index a jump table to access a service routine. For
example:
SERVICE LDX
*
*
JMPTAB JMP
BSVR
$0C
$1C
$00
$04
$08
$10
$14
$18
$20
NOP instructions are used only to align the JMP instructions 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. The first entry can be omitted since it
does not correspond to an interrupt.
JMP
NOP
JMP
NOP
JMP
NOP
.
.
.
JMP
END
I3
0
0
0
0
0
0
0
0
1
I2
0
0
0
0
1
1
1
1
0
BSVR
JMPTAB,XEnter service routine,
SERVE0Service condition #0
SERVE1Service condition #1
SERVE2Service condition #2
SERVE8Service condition #8
I1
0
0
1
1
0
0
1
1
0
I0
1
0
1
0
1
0
1
0
0
M68HC12B Family Data Sheet, Rev. 9.1
Fetch State Vector Number
(must end in an RTI)
Table 15-4. Interrupt Sources
Cyclical redundancy check (CRC) error
BDLC Tx data register empty (TDRE)
BDLC Rx data register full (RDRF)
Symbol invalid or out of range
Received IFR byte (RXIFR)
NOTE
No interrupts pending
Loss of arbitration
Interrupt Source
Received EOF
Wakeup
Freescale Semiconductor
8 (highest)
Priority
(lowest)
0
1
2
3
4
5
6
7