Datasheet

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
Section 18.4.5.5, “MSCAN Sleep Mode”). 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
0
INITAK
Initialization Mode Acknowledge — This flag indicates whether the MSCAN module is in initialization mode
(see Section 18.4.4.5, “MSCAN Initialization Mode”). 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
Module Base + 0x0002 Access: User read/write
1
1
Read: Anytime
Write: Anytime in initialization mode (INITRQ = 1 and INITAK = 1)
76543210
R
SJW1 SJW0 BRP5 BRP4 BRP3 BRP2 BRP1 BRP0
W
Reset: 00000000
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 Table 18-6).
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 Table 18-7).
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