P83CE558EBBSLASHYYY datasheet(22/72 Pages) PHILIPS

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Philips Semiconductors

Preliminary specification

P83CE558/P80CE558/P89CE558

Single-chip 8-bit microcontroller

1996 Aug 06

When Timer 0 is in Mode 3, Timer 1 can be programmed to operate

in Modes 0, 1 or 2 but cannot set an interrupt request flag or

generate an interrupt. However the overflow from Timer 1 can be

used to pulse the serial port baud-rate generator.

With a 16 MHz crystal, the counting frequency of these

timer/counters is as follows:

• In the timer function, the timer is incremented at a frequency of

1.33 MHz – a division by 12 of the system clock frequency

• 0 Hz to an upper limit of 0.66 MHz (1/24 of the system clock

frequency) when programmed for external inputs

Both internal and external inputs can be gated to the counter by a

second external source for directly measuring pulse durations.

When configured as a counter, the register is incremented on every

falling edge on the corresponding input pin, T0 or T1. The

incremented register value can be read earliest during the second

machine cycle after that one, during which the incrementing pulse

occurred.

The counters are started and stopped under software control. Each

one sets its interrupt request flag when it overflows from all HIGHs

to all LOWs (or automatic reload value), with the exception of mode

3 as previously described.

Figure 19. Timer/Counter mode control (TMOD) register.

TMOD (89H)

GATE

C/T

GATE

C/T

Timer 1

Timer 0

Table 12.

Description of TMOD bits

SYMBOL

BIT

FUNCTION

Gate

TMOD.7

TMOD.3

Gating control when set. Timer/Counter “x” is enabled only while “INTx” pin is high and “TRx” control pin is set.

When cleared Timer “x” is enabled whenever “TRx” control bit is set.

C/T

TMOD.6

TMOD.2

Timer or Counter Selector cleared for Timer operation (input from internal system clock). Set for Counter

operation (input from “Tx” input pin).

TMOD.5

TMOD.1

TMOD.4

TMOD.0

Timer 0, Timer 1 mode select see Table 13.

Table 13.

Timer 0 / Timer 1 operation select

OPERATING

8048 Timer “TLx” serves as 5-bit prescaler.

16-bit Timer/Counter “THx” and “TLx” are cascaded; there is no prescaler.

8-bit auto-reload Timer/Counter “THx” holds a value which is to be reloaded into “TLx” each time it overflows.

(Timer 0) TL0 is an 8-bit Timer/Counter controlled by the standard Timer 0 control bits. TH0 is an 8-bit timer

only controlled by Timer 1 control bits.

(Timer 1) Timer/Counter 1 stopped.

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