7630 datasheet(126/238 Pages) RENESAS

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7630 Group User’s Manual

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2.4 Controller Area Network (CAN) module

• Disabling auto-receive by setting CREC.6 causes the module to suspend all receive functions related to

the

receive control logic block (Figure 2.4.1) during the transmission process. The transmitting/receiving

sub-mode of the normal mode shown in Figure 2.4.25 is disabled.

Note: Disabling auto-receive does not affect the receive function related to the

protocol controller block

(required to monitor the bus level while transmitting).

2.4.9 Message transmission

The module is equipped with one transmit buffer. Similar to the receive section, the architecture allows to transmit

CAN frames on a one-by-one basis. Both standard and extended frame formats of data and remote type are sup-

ported. The programming sequence required to initiate a transmission comprises four steps, each step shall be

described in detail below:

1. Check the module status (i.e., the availability of the transmit buffer).

2. Initialize the transmit buffer (the buffer content defines the frame to be transmitted).

3. Lock the transmit buffer (hands the buffer control to the module and protects the buffer from accidental modifi-

cations by the CPU).

4. Issue the transmit request (triggers the module to start the transmission).

Once the transmission of a frame has been requested, the module takes care about bus arbitration, error handling

and acknowledgement of the frame by other nodes. The frame is considered transmitted successfully if:

• The frame could win arbitration,

• no errors were detected during transmission, and

• the frame gained acknowledgement by another node on the bus.

In case of unsuccessful transmissions the module attempts to re-transmit the frame until transmission can be fin-

ished successfully or the transmit request is withdrawn by user software (refer to section 2.4.10). In case of an arbi-

tration loss, the module transits to sub-mode receiving (refer to section 2.4.8 and Figure 2.4.26).

The programming sequence and functionality is explained below and by the flow charts in Figure 2.4.38.

(1) Check for availability of the transmit buffer

Before the transmit buffer can be initialized, its availability must be checked; the transmit buffer control bit

CTRM.5 must be “0” indicating the availability of the buffer and completion of the previous transmission. The

user software can now initialize the transmit buffer.

(2) Initialize the transmit buffer

In the user software the identifier (standard or extended), the frame type (data or remote frame), length

code/data bytes (in case of a data frame) have to be written to the transmit buffer (Figures 2.4.18 to 2.4.24).

Only the transmit buffer registers relevant for the specific CAN frame need to be initialized (e.g. if only stand-

ard CAN frames are concerned, the transmit buffer registers CTB2 and CTB3 can be ignored).

If the transmit buffer has been used for a previous transmission, the contents of the buffer are retained; there-

fore only the transmit buffer contents which need to be changed versus the previous frame have to be initial-

ized.

Figure 2.4.36 shows the transmit buffer register organisation.

7630 Datasheet(PDF) 126 Page - Renesas Technology Corp

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