Maxim-integrated High-Speed Microcontroller Users Guide: Network Mi Uživatelský manuál stáhnout pdf (Strana 164)

High-Speed Microcontroller User’s

Guide: Network Microcontroller

Supplement

164

Bus Rate Timing Example

The following table shows a few example bit timing settings for common oscillator frequency and baud-rate selections. Because of the

large number of variables, there are many combinations not shown that can achieve a desired baud rate. There are a number of

approaches to determining all the bit timing factors, but this uses the most common (i.e., the oscillator frequency and baud rate have

already been determined by system constraints.)

Additional Bit Timing Examples

The following is an explanation of how the table row illustrating an oscillator frequency of 16MHz and a CAN baud rate of 125kbps is

derived.

Various combinations of BRPV are selected until one is located that meets the t

per bit criteria, i.e., an integer value less than 25.

Selecting BRPV = 4, the previously described equations state that there should be 16 t

per bit. That leaves 16 – 1 or 15 t

remain-

ing for TS1_LEN and TS2_LEN, which are arbitrarily assigned as shown. Because BRPV > 3, the triple sampling feature (SMP = 1) can

be used, if desired.

FOSC

CCD BRPV TQU

BAUD

RATE

PER BIT

TS1_LEN

TS2_LEN

SJW

SMP = 1

PERMITTED?

2 2 100ns 1Mbps 10 5 4 3 NO

2 4 200ns 500kbps 10 5 4 3 YES

2 5 250ns 250kbps 16 10 5 4 YES

40MHz

2 10 500ns 125kbps 16 10 5 4 YES

0.5 2 125ns 1Mbps 16 10 5 4 NO

1 1 125ns 1Mbps 16 10 5 4 NO

2 1 125ns 1Mbps 8 4 3 2 NO

2 1 125ns 500kbps 16 10 5 4 NO

2 2 250ns 250kbps 16 10 5 4 NO

16MHz

2 4 500ns 125kbps 16 10 5 4 YES

1 1 125ns 1Mbps 8 4 3 2 NO

1 1 125ns 500kbps 16 10 5 4 NO

1 1 250ns 250kbps 16 10 5 4 NO

8MHz

2 2 500ns 125kbps 16 10 5 4 NO

Maxim Integrated

1 2 ... 159 160 161 162 163 164 165 166 167 168 169 ... 220 221

NETWORKED MICROCONTROLLER 1
Supplement 10

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