P89LPC938FA NXP Semiconductors, P89LPC938FA Datasheet - Page 34

• Manufacturer Part Number: P89LPC938FA
• Description: IC, MCU 8BIT 80C51 8K FLASH, PLCC28
• Manufacturer: NXP Semiconductors

Specifications of P89LPC938FA

• Controller Family/series: (8051) 8052
• Core Size: 8bit
• No. Of I/o's: 26
• Program Memory Size: 8KB
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 768Byte
• Cpu Speed: 18MHz
• Oscillator Type: External,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Philips Semiconductors
9397 750 14051
Product data sheet
7.20.10 The 9
7.20.8 Double buffering
7.20.9 Transmit interrupts with double buffering enabled (Modes 1, 2 and 3)
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).
Unlike the conventional UART, in double buffering mode, the Tx interrupt is generated
when the double buffer is ready to receive new data.
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.
th
bit (bit 8) in double buffering (Modes 1, 2 and 3)
Rev. 01 — 25 February 2005
8-bit microcontroller with 10-bit A/D converter
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
P89LPC938
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