UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
57 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
10.6 Baud Rate generator and selection
The P89LPC980/982 enhanced UART has an independent Baud Rate Generator. The
baud rate is determined by a value programmed into the BRGR1 and BRGR0 SFRs. The
UART can use either Timer 1 or the baud rate generator output as determined by
BRGCON[2:1] (see
). Note that Timer T1 is further divided by 2 if the SMOD1 bit
(PCON.7) is set. The independent Baud Rate Generator uses CCLK.
10.7 Updating the BRGR1 and BRGR0 SFRs
The baud rate SFRs, BRGR1 and BRGR0 must only be loaded when the Baud Rate
Generator is disabled (the BRGEN bit in the BRGCON register is logic 0). This avoids the
loading of an interim value to the baud rate generator.
(CAUTION: If either BRGR0 or
BRGR1 is written when BRGEN = 1, the result is unpredictable.)
Table 44.
UART SFR addresses
Register
Description
SFR location
PCON
Power Control
87H
SCON
Serial Port (UART) Control
98H
SBUF
Serial Port (UART) Data Buffer
99H
SADDR
Serial Port (UART) Address
A9H
SADEN
Serial Port (UART) Address Enable
B9H
SSTAT
Serial Port (UART) Status
BAH
BRGR1
Baud Rate Generator Rate High Byte
BFH
BRGR0
Baud Rate Generator Rate Low Byte
BEH
BRGCON
Baud Rate Generator Control
BDH
Table 45.
UART baud rate generation
SCON.7
(SM0)
SCON.6
(SM1)
PCON.7
(SMOD1)
BRGCON.1
(SBRGS)
Receive/transmit baud rate for UART
0
0
X
X
CCLK
⁄
16
0
1
0
0
CCLK
⁄
(256-TH1)64
1
0
CCLK
⁄
(256-TH1)32
X
1
CCLK
⁄
((BRGR1,BRGR0)+16)
1
0
0
X
CCLK
⁄
32
1
X
CCLK
⁄
16
1
1
0
0
CCLK
⁄
(256-TH1)64
1
0
CCLK
⁄
(256-TH1)32
X
1
CCLK
⁄
((BRGR1,BRGR0)+16)
Table 46.
Baud Rate Generator Control register (BRGCON - address BDh) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
--
-
-
-
-
-
SBRGS
BRGEN
Reset
x
x
x
x
x
x
0
0