P89LPC913 datasheet(40/66 Pages) NXP

40 / 66 page

P89LPC912_913_914_5

Product data sheet

Rev. 05 — 28 September 2007

40 of 66

NXP Semiconductors

P89LPC912/913/914

8-bit microcontrollers with two-clock 80C51 core

8.18.2 Mode 1

10 bits are transmitted (through TXD) or received (through RXD): a start bit (logic 0),

8 data bits (LSB ﬁrst), and a stop bit (logic 1). When data is received, the stop bit is stored

in RB8 in Special Function Register SCON. The baud rate is variable and is determined

by the Timer 1 overﬂow rate or the Baud Rate Generator (described in Section 8.18.5

“Baud rate generator and selection”).

8.18.3 Mode 2

11 bits are transmitted (through TXD) or received (through RXD): start bit (logic 0), 8 data

bits (LSB ﬁrst), a programmable 9th data bit, and a stop bit (logic 1). When data is

transmitted, the 9th data bit (TB8 in SCON) can be assigned the value of logic 0 or logic 1.

Or, for example, the parity bit (P, in the PSW) could be moved into TB8. When data is

received, the 9th data bit goes into RB8 in Special Function Register SCON, while the stop

bit is not saved. The baud rate is programmable to either 1

⁄

16 or

⁄

32 of the CCLK

frequency, as determined by the SMOD1 bit in PCON.

8.18.4 Mode 3

11 bits are transmitted (through TXD) or received (through RXD): a start bit (logic 0), 8

data bits (LSB ﬁrst), a programmable 9th data bit, and a stop bit (logic 1). In fact, 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 (described in

section Section 8.18.5 “Baud rate generator and selection”).

8.18.5 Baud rate generator and selection

The P89LPC913 and P89LPC914 devices have an independent Baud Rate Generator.

The baud rate is determined by a baud-rate preprogrammed into the BRGR1 and BRGR0

SFRs which together form a 16-bit baud rate divisor value that works in a similar manner

as Timer 1. If the baud rate generator is used, Timer 1 can be used for other timing

functions.

The UART can use either Timer 1 or the baud rate generator output (see Figure 15). Note

that Timer T1 is further divided by 2 if the SMOD1 bit (PCON.7) is cleared. The

independent Baud Rate Generator uses CCLK.

8.18.6 Framing error

Framing error is reported in the status register (SSTAT). In addition, if SMOD0 (PCON.6)

is logic 1, framing errors can be made available in SCON.7, respectively. If SMOD0 is

logic 0, SCON.7 is SM0. It is recommended that SM0 and SM1 (SCON[7:6]) are set up

when SMOD0 is logic 0.

Fig 15. Baud rate sources for UART (Modes 1, 3)

baud rate modes 1 and 3

SBRGS = 1

SBRGS = 0

SMOD1 = 0

SMOD1 = 1

timer 1 overflow

(PCLK-based)

baud rate generator

(CCLK-based)

002aaa419

÷2

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