P89LPC970FDH datasheet(33/67 Pages) NXP

33 / 67 page

P89LPC97X

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Product data sheet

Rev. 3 — 8 June 2010

33 of 66

NXP Semiconductors

P89LPC970/971/972

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

7.22.7 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.

7.22.8 Double buffering

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

written to SnBUF 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

SBUF 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).

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

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

when the double buffer is ready to receive new data.

7.22.10 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 TI interrupt.

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

double-buffered together with SBUF data.

7.23 I2C-bus serial interface

The I2C-bus uses two wires (SDA and SCL) to transfer information between devices

connected to the bus, and it has the following features:

• Bidirectional data transfer between masters and slaves

• Multi master bus (no central master)

• Arbitration between simultaneously transmitting masters without corruption of serial

data on the bus

• Serial clock synchronization allows devices with different bit rates to communicate via

one serial bus

• Serial clock synchronization can be used as a handshake mechanism to suspend and

resume serial transfer

• The I2C-bus may be used for test and diagnostic purposes.

A typical I2C-bus configuration is shown in Figure 8. The P89LPC970/971/972 device

provides a byte-oriented I2C-bus interface that supports data transfers up to 400 kHz.

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