80C186EC/80C188EC Microprocessor User's Manual

SERIAL COMMUNICATIONS UNIT
Register Name:
Register Mnemonic:
Register Function:
Baud Rate Compare Register
BxCMP
Determines baud rate for the serial port.
15 0
I
C
L
K
B
R
1
4
B
R
1
3
B
R
1
2
B
R
1
1
B
R
1
0
B
R
9
B
R
8
B
R
7
B
R
6
B
R
5
B
R
4
B
R
3
B
R
2
B
R
1
B
R
0
A1276-0A
Bit
Mnemonic
Bit Name
Reset
State
Function
ICLK
BR14:0
Internal
Clocking
Baud Rate
Compare
Field
0 Selects the input clock:
0 = BCLK is input to baud clock.
1 = CPU clock is input to baud clock.
0 Sets the compare value for the baud rate clock.
Figure 11-11. Baud Rate Compare Register (BxCMP)
The equations in Figure 11-12 show how to calculate the proper BxCMP value for a specific baud
rate (where F CPU = CPU operating frequency = ½ CLKIN frequency).
Mode 0 Mode 1–4
If CPU clock is baud timebase clock:
BxCMP
F CPU
= -------------------------- – 1 BxCMP =
baudrate
F CPU
----------------------------------- – 1
baudrate × 8
If BCLK is baud timebase clock:
BxCMP
BCLK
BCLK
= -------------------------- B x CMP = -----------------------------------
baudrate
baudrate × 8
Figure 11-12. Calculating the BxCMP Value for a Specific Baud Rate
11-12