P89LPC9401_1 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Preliminary data sheet Rev. 01 — 5 September 2005 26 of 59
Philips Semiconductors
P89LPC9401
8-bit two-clock 80C51 microcontroller with 32 segment × 4 LCD driver
7.17.5 Mode 6
In this mode, the corresponding timer can be changed to a PWM with a full period of
256 timer clocks.
7.17.6 Timer overflow toggle output
Timers 0 and 1 can be configured to automatically toggle a port output whenever a timer
overflow occurs. The same device pins that are used for the T0 and T1 count inputs are
also used for the timer toggle outputs. The port outputs will be a logic 1 prior to the first
timer overflow when this mode is turned on.
7.18 RTC/system timer
The P89LPC9401 has a simple RTC that allows a user to continue running an accurate
timer while the rest of the device is powered-down. The RTC can be a wake-up or an
interrupt source. The RTC is a 23-bit down counter comprised of a 7-bit prescaler and a
16-bit loadable down counter. When it reaches all logic 0s, the counter will be reloaded
again and the RTCF flag will be set. The clock source for this counter can be either the
CCLK or the XTAL oscillator, provided that the XTAL oscillator is not being used as the
CPU clock. If the XTAL oscillator is used as the CPU clock, then the RTC will use CCLK as
its clock source. Only power-on reset will reset the RTC and its associated SFRs to the
default state.
7.19 UART
The P89LPC9401 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
P89LPC9401 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
four modes: shift register, 8-bit UART, 9-bit UART, and CPU clock/32 or CPU clock/16.
7.19.1 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.
7.19.2 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 7.19.5
“Baud rate generator and selection”).
7.19.3 Mode 2
11 bits are transmitted (through TXD) or received (through RXD): start bit (logic 0), 8 data
bits (LSB first), a programmable 9
th
data bit, and a stop bit (logic 1). When data is
transmitted, the 9
th
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
