HC05 datasheet(78/232 Pages) MOTOROLA

78 / 232 page

MOTOROLA

5-16

MC68HC05X16

Rev. 1

MOTOROLA CAN MODULE (MCAN)

5.3.8

MCAN bus timing register 1 (CBT1)

This register can only be accessed when the reset request bit in the CCNTRL register is set.

SAMP — Sampling

This bit determines the number of samples of the serial bus to be taken per bit time. When set three

samples per bit are taken. This sample rate gives better rejection of noise on the bus, but

introduces a one bit delay to the bus sampling. For higher bit rates SAMP should be cleared, which

means that only one sample will be taken per bit.

1 (set)

–

Three samples per bit.

0 (clear) –

One sample per bit.

TSEG22 – TSEG10 — Time segment bits

Time segments within the bit time ﬁx the number of clock cycles per bit time, and the location of

the sample point.

SYNC_SEG

System expects transitions to occur on the bus during this period.

Transmit point

A node in transmit mode will transfer a new value to the MCAN bus at this point.

Sample point

A node in receive mode will sample the bus at this point. If the three samples per

bit option is selected then this point marks the position of the third sample.

Time segment 1 (TSEG1) and time segment 2 (TSEG2) are programmable as shown in Table 5-3.

The bit time is determined by the oscillator frequency, the baud rate prescaler, and the number of

bus clock cycles (tSCL) per bit (as shown above).

Address

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

State

on reset

MCAN bus timing 1 (CBT1)

$0027

SAMP TSEG22 TSEG21 TSEG20TSEG13TSEG12TSEG11TSEG10 Undeﬁned

Figure 5-5 Segments within the bit time

TSEG 1

BIT_TIME

SYNC_SEG

TSEG 2

SYNC_SEG

1 clock cycle

tSCL

Sample point

Transmit point

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