How To Use The Baud Rate Timer - Panasonic MN101C00 User Manual

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)
compare register set value = timer clock frequency/(baud rate 2 8) – 1
Table 5-3-1 UART Transfer Rate
Transfer Speed
300
(bps)
fosc
Set
(MHz)
Value
fosc
—
4.0
fs/4
104
fs/16
—
fosc
—
4.19
fs/4
109
fs/16
—
fosc
—
8.0
fs/4
208
fs/16
—
fosc
—
8.38
fs/4
218
fs/16
—
fosc
—
12.0
fs/4
—
fs/16
78
fosc
—
16.0
fs/4
—
fs/16
104
fosc
—
16.76
fs/4
—
fs/16
109
fosc
—
20.0
fs/4
—
fs/16
130
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 10
SC0MD1(SC0CKM)
1200 2400
Calculated Set Calculated Set Calculated
Value Value
Value Value Value
— 208 1202 104 2403
300 — — —
— — — —
— 218 1201 109 2402
300 — — —
— — — —
— — — 208 2404
300 52 1201 —
— — — —
— — — 218 2403
300 55 1190 —
— — — —
— — — —
— 78 1202 39 2403
300 — — —
— — — —
— 104 1202 52 2404
300 — — —
— — — —
— 109 1201 55 2381
300 — — —
— — — —
— 130 1202 65 2404
300 — — —
6 /2/4)/(300 2 8) – 1
=207
= X'CF'
4800 9600
Set Calculated Set Calculated
Value Value
Value Value
52 4807 26 9615
— — — — —
— — — — —
55 4761 27 9699
— — — — —
— — — — —
104 4807 52 9615
— — — — —
— — — — —
109 4805 55 9523
— — — — —
— — — — —
— 156 4808 78 9615
— — — —
— — — — —
— 208 4808 104 9615
— — — —
— — — — —
— 218 4805 109 9610
— — — —
— — — — —
— — — 130 9615
33 4735 — —
— — — — —
Chapter 5 Serial Functions
Set the values from this table
19200
(minus 1) in the compare
Set Calculated
register.
Value
Value
13 19230
— —
— —
— —
— —
— —
26 19230
— —
— —
27 19398
— —
— —
39 19230
— —
— —
52 19230
— —
— —
55 19045
— —
— —
65 19231
— —
— —
Half-duplex UART Serial Interface
105