PXD10RM Datasheet, PDF (177/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

7.4.1 Enabling/disabling the CAN Sampler
The CAN sampler is disabled on reset and the CPU is able to access the 12 registers used for storing
samples. The CAN Sampler must be enabled before entering standby or stop mode by setting
CR[CAN_SMPLR_EN].
When the CAN sampler is enabled, the A, D, WEN, CSN and CK to the (12 x 32) block of registers are
switched to those generated by the kernel of the sampler. You can monitor CR[Active_CK] to check which
is the active clock to the registers.
Any activity on selected Rx line, the sampler enables the 16 MHz RC oscillator. When CAN_SMPLR_EN
is reset to 0, the sampler should at least receive 3 RC clock pulses to reset itself, after which the RC can
be switched off.
When the software wishes to access the sample registers contents it must first reset the CAN_SMPLR_EN
bit by writing a ‘0’. Before accessing the register contents it must monitor Active_CK bit for ‘0’.When this
bit is reset it can safely access the (12 x 32) sample registers. While shifting from normal to sample mode
and vice versa, the sample register signals must be static and inactive to ensure the data is not corrupt.
7.4.2 Selecting the Rx port
One Rx port can be selected per sampling routine; the port to be sampled is selected by CAN_RX_SEL.
Table 7-3. Internal multiplexer correspondence
CAN_RX_SEL
000
001
010
011
100
101
110
111
Rx selected
CANRX_0 PB[1]
CANRX_1 PB[10]
CANRX_2 PF[13]
CANRX_3 PJ[4]
CANRX_4 PJ[6]
Reserved
Reserved
Reserved
7.4.3 Baud rate generation
Sampling is performed at a baud rate that is set by the software as a multiple of RC oscillator frequency of
62.5 ns (assuming RC is configured for high frequency mode i.e. 16 MHz). User must set the baud rate
prescaler (BRP) such that 8 samples per bit are achieved.
Baud rate setting must be made by software before going into standby or stop mode. This is done by setting
BRP bits 5:1 in Control register. The reset value of BRP is 00000 and can be set to max. 11111 which gives
a prescale value of BRP+1 thus providing a BRP range of 1 to 32.
• Max. bitrate supported for sampling is 2Mbps using BRP as 1
• Min. bitrate supported for sampling is 62.5kbps using BRP as 32
PXD10 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
7-5
Preliminary—Subject to Change Without Notice