Freescale Semiconductor MC9S12ZVHL32, Справочное руководство

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Chapter 11 Freescale’s Scalable Controller Area Network (S12MSCANV3)
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
Freescale Semiconductor 429
3
TIME
Timer Enable — This bit activates an internal 16-bit wide free running timer which is clocked by the bit clock rate.
If the timer is enabled, a 16-bit time stamp will be assigned to each transmitted/received message within the
active TX/RX buffer. Right after the EOF of a valid message on the CAN bus, the time stamp is written to the
highest bytes (0x000E, 0x000F) in the appropriate buffer (see
Section 11.3.3, “Programmer’s Model of Message
Storage ”). In loopback mode no receive timestamp is generated. The internal timer is reset (all bits set to 0) when
disabled. This bit is held low in initialization mode.
0 Disable internal MSCAN timer
1 Enable internal MSCAN timer
2
WUPE
(3)
Wake-Up Enable — This configuration bit allows the MSCAN to restart from sleep mode or from power down
mode (entered from sleep) when traffic on CAN is detected (see Section 11.4.5.5, “MSCAN Sleep Mode ”). This
bit must be configured before sleep mode entry for the selected function to take effect.
0 Wake-up disabled — The MSCAN ignores traffic on CAN
1 Wake-up enabled — The MSCAN is able to restart
1
SLPRQ
(4)
Sleep Mode Request — This bit requests the MSCAN to enter sleep mode, which is an internal power saving
mode (see Section 11.4.5.5, “MSCAN Sleep Mode ”). The sleep mode request is serviced when the CAN bus is
idle, i.e., the module is not receiving a message and all transmit buffers are empty. The module indicates entry
to sleep mode by setting SLPAK = 1 (see
Section 11.3.2.2, “MSCAN Control Register 1 (CANCTL1) ”). SLPRQ
cannot be set while the WUPIF flag is set (see Section 11.3.2.5, “MSCAN Receiver Flag Register (CANRFLG) ”).
Sleep mode will be active until SLPRQ is cleared by the CPU or, depending on the setting of WUPE, the MSCAN
detects activity on the CAN bus and clears SLPRQ itself.
0 Running — The MSCAN functions normally
1 Sleep mode request — The MSCAN enters sleep mode when CAN bus idle
0
INITRQ
(5),(6)
Initialization Mode Request — When this bit is set by the CPU, the MSCAN skips to initialization mode (see
Section 11.4.4.5, “MSCAN Initialization Mode ”). Any ongoing transmission or reception is aborted and
synchronization to the CAN bus is lost. The module indicates entry to initialization mode by setting INITAK = 1
(
Section 11.3.2.2, “MSCAN Control Register 1 (CANCTL1) ”).
The following registers enter their hard reset state and restore their default values: CANCTL0
(7)
, CANRFLG
(8)
,
CANRIER
(9)
, CANTFLG, CANTIER, CANTARQ, CANTAAK, and CANTBSEL.
The registers CANCTL1, CANBTR0, CANBTR1, CANIDAC, CANIDAR0-7, and CANIDMR0-7 can only be
written by the CPU when the MSCAN is in initialization mode (INITRQ = 1 and INITAK = 1). The values of the
error counters are not affected by initialization mode.
When this bit is cleared by the CPU, the MSCAN restarts and then tries to synchronize to the CAN bus. If the
MSCAN is not in bus-off state, it synchronizes after 11 consecutive recessive bits on the CAN bus; if the MSCAN
is in bus-off state, it continues to wait for 128 occurrences of 11 consecutive recessive bits.
Writing to other bits in CANCTL0, CANRFLG, CANRIER, CANTFLG, or CANTIER must be done only after
initialization mode is exited, which is INITRQ = 0 and INITAK = 0.
0 Normal operation
1 MSCAN in initialization mode
1. See the Bosch CAN 2.0A/B specification for a detailed definition of transmitter and receiver states.
2. In order to protect from accidentally violating the CAN protocol, TXCAN is immediately forced to a recessive state when the
CPU enters wait (CSWAI = 1) or stop mode (see Section 11.4.5.2, “Operation in Wait Mode ” and Section 11.4.5.3, “Operation
in Stop Mode ”)
.
3. The CPU has to make sure that the WUPE register and the WUPIE wake-up interrupt enable register (see Section 11.3.2.6,
“MSCAN Receiver Interrupt Enable Register (CANRIER) ) is enabled, if the recovery mechanism from stop or wait is required.
4. The CPU cannot clear SLPRQ before the MSCAN has entered sleep mode (SLPRQ = 1 and SLPAK = 1).
5. The CPU cannot clear INITRQ before the MSCAN has entered initialization mode (INITRQ = 1 and INITAK = 1).
6. In order to protect from accidentally violating the CAN protocol, TXCAN is immediately forced to a recessive state when the
initialization mode is requested by the CPU. Thus, the recommended procedure is to bring the MSCAN into sleep mode
(SLPRQ = 1 and SLPAK = 1) before requesting initialization mode.
7. Not including WUPE, INITRQ, and SLPRQ.
8. TSTAT1 and TSTAT0 are not affected by initialization mode.
Table 11-2. CANCTL0 Register Field Descriptions (continued)
Field Description