UM10310_1 © NXP B.V. 2008. All rights reserved.
User manual Rev. 01 — 1 December 2008 60 of 139
NXP Semiconductors UM10310
P89LPC9321 User manual
10.4 Mode 3
11 bits are transmitted (through TXD) or received (through RXD): a start bit (logic0), 8
data bits (LSB first), a programmable 9th data bit, and a stop bit (logic1). Mode 3 is the
same as Mode 2 in all respects except baud rate. The baud rate in Mode 3 is variable and
is determined by the Timer 1 overflow rate or the Baud Rate Generator (see Section 10.6
Baud Rate generator and selection).
In all four modes, transmission is initiated by any instruction that uses SBUF as a
destination register. Reception is initiated in Mode 0 by the condition RI = 0 and REN = 1.
Reception is initiated in the other modes by the incoming start bit if REN = 1.
10.5 SFR space
The UART SFRs are at the following locations:
10.6 Baud Rate generator and selection
The P89LPC9321 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 Figure 26). 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 logic0). 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 51. 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 52. UART baud rate generation
SCON.7
(SM0) SCON.6
(SM1) PCON.7
(SMOD1) BRGCON.1
(SBRGS) Receive/transmit baud rate for UART
00XX CCLK16
0100 CCLK(256-TH1)64
10 CCLK(256-TH1)32
X1 CCLK((BRGR1,BRGR0)+16)