C515C_9711 Datasheet, PDF (172/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.5.8 Switch-off Capability of the CAN Controller (C515C-8E only)
For power consumption reasons, the on-chip CAN controller in the C515C-8E can be switched off
by setting bit CSWO in SFR SYSCON. When the CAN controller is switched off its clock signal is
turned off and the operation of the CAN controller is stopped. This switch-off state of the CAN
controller is equal to its state in software power down mode. Any message transfer is interrupted.
In order to ensure that the CAN controller is not stopped while sending a dominant level (“0”) on the
CAN bus, the microcontroller should set bit INIT in the Control Register prior to setting bit CSWO.
The C515C-8E can check, if a transmission is in progress by reading bits TXRQ and NEWDAT in
the message objects and bit TXOK in the Control Register. After clearing bit CSWO again the CAN
controller has to be reconfigured.
Special Function Register SYSCON (Address B1H)
Reset Value : XX100001B
Bit No. MSB
LSB
7
6
5
4
3
2
1
0
B1H
– PMOD EALE RMAP – _CSWO XMAP1 XMAP0 SYSCON
The functions of the shaded bits are not described in this section.
Bit
–
CSWO
Function
Reserved bits for future use. Read by CPU returns undefined values.
CAN controller switch-off bit
CSWO = 0 : CAN controller is enabled (default after reset).
CSWO = 1 : CAN controller is switched off.
When the C515C-8E is put into software power down mode, bit CSWO is not affected. This means,
when software power down mode is entered with CAN controller switched off, the CAN controller
stays in switch-off state after the wake-up from software power down mode has been left.
Semiconductor Group
6-109
1997-11-01