P87LPC779FDH datasheet(45/74 Pages) PHILIPS

45 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

45 of 74

9397 750 13213

8.14.5

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. This function is enabled by control

bits ENT0 and ENT1 in the P2M1 register, and apply to Timer0 and Timer1

respectively. The port outputs will be a logic 1 prior to the ﬁrst timer overﬂow when

this mode is turned on.

8.15 UART

The P87LPC779 includes an enhanced 80C51 UART. The baud rate source for the

UART is Timer1 for modes 1 and 3, while the rate is ﬁxed in modes 0 and 2. Because

CPU clocking is different on the P87LPC779 than on the standard 80C51, baud rate

calculation is somewhat different. Enhancements over the standard 80C51 UART

include Framing Error detection and automatic address recognition.

The serial port is full duplex, meaning it can transmit and receive simultaneously. It is

also receive-buffered, meaning it can commence reception of a second byte before a

previously received byte has been read from the SBUF register. However, if the ﬁrst

byte still hasn’t been read by the time reception of the second byte is complete, the

ﬁrst byte will be lost. The serial port receive and transmit registers are both accessed

through Special Function Register SBUF. Writing to SBUF loads the transmit register,

and reading SBUF accesses a physically separate receive register.

The serial port can be operated in 4 modes.

Fig 22. Timer/counter 0 Mode 3 (two 8-bit counters).

002aaa640

Osc/6

or Osc/12

Osc/6

or Osc/12

T0 pin

TR0

TR1

Gate

INT0 pin

C/T = 0

C/T = 1

TL0

(8-bits)

TF0

control

T0OE

T0 pin

toggle

overflow

interrupt

TH0

(8-bits)

TF1

control

T1OE

T1 pin

toggle

overflow

interrupt

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