P89LPC9402 datasheet(29/60 Pages) NXP

29 / 60 page

P89LPC9402_1

Product data sheet

Rev. 01 — 22 April 2009

29 of 60

NXP Semiconductors

P89LPC9402

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

7.20.7 Break detect

Break detect is reported in the status register (SSTAT). A break is detected when

11 consecutive bits are sensed LOW. The break detect can be used to reset the device

and force the device into ISP mode.

7.20.8 Double buffering

The UART has a transmit double buffer that allows buffering of the next character to be

written to SBUF while the ﬁrst character is being transmitted. Double buffering allows

transmission of a string of characters with only one stop bit between any two characters,

as long as the next character is written between the start bit and the stop bit of the

previous character.

Double buffering can be disabled. If disabled (DBMOD, i.e., SSTAT.7 = 0), the UART is

compatible with the conventional 80C51 UART. If enabled, the UART allows writing to

SnBUF while the previous data is being shifted out. Double buffering is only allowed in

Modes 1, 2 and 3. When operated in Mode 0, double buffering must be disabled

(DBMOD = 0).

7.20.9 Transmit interrupts with double buffering enabled (modes 1, 2 and 3)

Unlike the conventional UART, in double buffering mode, the TX interrupt is generated

when the double buffer is ready to receive new data.

7.20.10 The 9th bit (bit 8) in double buffering (modes 1, 2 and 3)

If double buffering is disabled TB8 can be written before or after SBUF is written, as long

as TB8 is updated some time before that bit is shifted out. TB8 must not be changed until

the bit is shifted out, as indicated by the TX interrupt.

If double buffering is enabled, TB8 must be updated before SBUF is written, as TB8 will

be double-buffered together with SBUF data.

P89LPC9402 Datasheet(PDF) 29 Page - NXP Semiconductors