Panasonic MN101C00 user manual How to Use the Baud Rate Timer

5-3-3 How to Use the Baud Rate Timer

Refer to the following when using the baud rate timer to set the UART transfer speed.

(1)Specifying the timer clock source

The clock source is specified by the TM3CKS3 to 1 flags of the timer 3 mode register (TM3MD).

(2)Setting the compare register

The compare register value is set in the timer 3 compare register (TM3OC).

This set value is computed according to the following formula: overflow period = (compare register set value + 1) ⋅ timer clock period baud rate = 1/(overflow period ⋅ 2 ⋅ 8)

↑SC0MD1(SC0CKM)

	compare register set value = timer clock frequency/(baud rate ⋅ 2 ⋅ 8) – 1
		Table 5-3-1 UART Transfer Rate
Transfer Speed		300		1200		2400		4800		9600		19200
fosc	(bps)
		Set	Calculated	Set	Calculated	Set	Calculated	Set	Calculated	Set	Calculated	Set	Calculated
(MHz)
		Value	Value	Value	Value	Value	Value	Value	Value	Value	Value	Value	Value
4.0	fosc	—	—	208	1202	104	2403	52	4807	26	9615	13	19230
	fs/4	104	300	—	—	—	—	—	—	—	—	—	—
	fs/16	—	—	—	—	—	—	—	—	—	—	—	—
4.19	fosc	—	—	218	1201	109	2402	55	4761	27	9699	—	—
	fs/4	109	300	—	—	—	—	—	—	—	—	—	—
	fs/16	—	—	—	—	—	—	—	—	—	—	—	—
8.0	fosc	—	—	—	—	208	2404	104	4807	52	9615	26	19230
	fs/4	208	300	52	1201	—	—	—	—	—	—	—	—
	fs/16	—	—	—	—	—	—	—	—	—	—	—	—
8.38	fosc	—	—	—	—	218	2403	109	4805	55	9523	27	19398
	fs/4	218	300	55	1190	—	—	—	—	—	—	—	—
	fs/16	—	—	—	—	—	—	—	—	—	—	—	—
	fosc	—	—	—	—	—	—	156	4808	78	9615	39	19230
12.0	fs/4	—	—	78	1202	39	2403	—	—	—	—	—	—
	fs/16	78	300	—	—	—	—	—	—	—	—	—	—
16.0	fosc	—	—	—	—	—	—	208	4808	104	9615	52	19230
	fs/4	—	—	104	1202	52	2404	—	—	—	—	—	—
	fs/16	104	300	—	—	—	—	—	—	—	—	—	—
16.76	fosc	—	—	—	—	—	—	218	4805	109	9610	55	19045
	fs/4	—	—	109	1201	55	2381	—	—	—	—	—	—
	fs/16	109	300	—	—	—	—	—	—	—	—	—	—
20.0	fosc	—	—	—	—	—	—	—	—	130	9615	65	19231
	fs/4	—	—	130	1202	65	2404	33	4735	—	—	—	—
	fs/16	130	300	—	—	—	—	—	—	—	—	—	—

Example:

The timer 3 clock source is fs/4 (fosc = 8MHz) and a baud rate of 300 bps is

desired.

Since fs=fosc/2,

compare register set value = (8 ⋅ 106/2/4)/(300 ⋅ 2 ⋅ 8) – 1

=207

= X'CF'

Chapter 5 Serial Functions

Set the values from this table

(minus 1) in the compare

register.

Half-duplex UART Serial Interface 105