89LPC925 View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

89LPC925

8-bit microcontrollers with accelerated two-clock 80C51 core 4 kB/8 kB 3 V low-power Flash with 8-bit A/D converter

Philips Electronics 

Philips Semiconductors

P89LPC924/925

8-bit microcontrollers with accelerated two-clock 80C51 core

9397 750 13459

Product data

8.19 UART

The P89LPC924/925 has an enhanced UART that is compatible with the

conventional 80C51 UART except that Timer 2 overflow cannot be used as a baud

rate source. The P89LPC924/925 does include an independent Baud Rate

Generator. The baud rate can be selected from the oscillator (divided by a constant),

Timer 1 overflow, or the independent Baud Rate Generator. In addition to the baud

rate generation, enhancements over the standard 80C51 UART include Framing

Error detection, automatic address recognition, selectable double buffering and

several interrupt options.The UART can be operated in 4 modes: shift register, 8-bit

UART, 9-bit UART, and CPU clock/32 or CPU clock/16.

8.19.1 Mode 0

Serial data enters and exits through RxD. TxD outputs the shift clock. 8 bits are

transmitted or received, LSB first. The baud rate is fixed at 1⁄16 of the CPU clock

frequency.

8.19.2 Mode 1

10 bits are transmitted (through TxD) or received (through RxD): a start bit

(logical ‘0’), 8 data bits (LSB first), and a stop bit (logical ‘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 8.19.5 “Baud rate generator and selection”).

8.19.3 Mode 2

11 bits are transmitted (through TxD) or received (through RxD): start bit (logical ‘0’),

8 data bits (LSB first), a programmable 9th data bit, and a stop bit (logical ‘1’). When

data is transmitted, the 9th data bit (TB8 in SCON) can be assigned the value of ‘0’ or

‘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 1⁄32 of

the CPU clock frequency, as determined by the SMOD1 bit in PCON.

8.19.4 Mode 3

11 bits are transmitted (through TxD) or received (through RxD): a start bit

(logical ‘0’), 8 data bits (LSB first), a programmable 9th data bit, and a stop bit

(logical ‘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 8.19.5 “Baud rate generator and

selection”).

8.19.5 Baud rate generator and selection

The P89LPC924/925 enhanced UART has 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 but is much more accurate. 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 7).

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

independent Baud Rate Generator uses OSCCLK.

Rev. 02 — 15 June 2004

© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

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