Freescale Semiconductor Tower System Module S12G240 TWR-S12G240 TWR-S12G240 Data Sheet
Product codes
TWR-S12G240
Freescale’s Scalable Controller Area Network (S12MSCANV3)
MC9S12G Family Reference Manual,
Rev.1.23
594
Freescale Semiconductor
18.3.2.3
MSCAN Bus Timing Register 0 (CANBTR0)
The CANBTR0 register configures various CAN bus timing parameters of the MSCAN module.
1
SLPAK
Sleep Mode Acknowledge — This flag indicates whether the MSCAN module has entered sleep mode (see
”). It is used as a handshake flag for the SLPRQ sleep mode request.
Sleep mode is active when SLPRQ = 1 and SLPAK = 1. Depending on the setting of WUPE, the MSCAN will
clear the flag if it detects activity on the CAN bus while in sleep mode.
0 Running — The MSCAN operates normally
1 Sleep mode active — The MSCAN has entered sleep mode
clear the flag if it detects activity on the CAN bus while in sleep mode.
0 Running — The MSCAN operates normally
1 Sleep mode active — The MSCAN has entered sleep mode
0
INITAK
Initialization Mode Acknowledge — This flag indicates whether the MSCAN module is in initialization mode
(see
(see
”). It is used as a handshake flag for the INITRQ initialization
mode request. Initialization mode is active when INITRQ = 1 and INITAK = 1. The registers CANCTL1,
CANBTR0, CANBTR1, CANIDAC, CANIDAR0–CANIDAR7, and CANIDMR0–CANIDMR7 can be written only by
the CPU when the MSCAN is in initialization mode.
0 Running — The MSCAN operates normally
1 Initialization mode active — The MSCAN has entered initialization mode
CANBTR0, CANBTR1, CANIDAC, CANIDAR0–CANIDAR7, and CANIDMR0–CANIDMR7 can be written only by
the CPU when the MSCAN is in initialization mode.
0 Running — The MSCAN operates normally
1 Initialization mode active — The MSCAN has entered initialization mode
Module Base + 0x0002
Access: User read/write
1
1
Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
7
6
5
4
3
2
1
0
R
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
W
Reset:
0
0
0
0
0
0
0
0
Figure 18-6. MSCAN Bus Timing Register 0 (CANBTR0)
Table 18-5. CANBTR0 Register Field Descriptions
Field
Description
7-6
SJW[1:0]
Synchronization Jump Width — The synchronization jump width defines the maximum number of time quanta
(Tq) clock cycles a bit can be shortened or lengthened to achieve resynchronization to data transitions on the
CAN bus (see
(Tq) clock cycles a bit can be shortened or lengthened to achieve resynchronization to data transitions on the
CAN bus (see
5-0
BRP[5:0]
Baud Rate Prescaler — These bits determine the time quanta (Tq) clock which is used to build up the bit timing
(see
(see
).
Table 18-6. Synchronization Jump Width
SJW1
SJW0
Synchronization Jump Width
0
0
1 Tq clock cycle
0
1
2 Tq clock cycles
1
0
3 Tq clock cycles
1
1
4 Tq clock cycles
Table 18-4. CANCTL1 Register Field Descriptions (continued)
Field
Description