P89C668 datasheet(39/89 Pages) PHILIPS

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Philips Semiconductors

Product data

P89C660/P89C662/P89C664/

P89C668

80C51 8-bit Flash microcontroller family

16KB/32KB/64KB ISP/IAP Flash with 512B/1KB/2KB/8KB RAM

2002 Oct 28

When Timer 2 is in the baud rate generator mode, one should not try

to read or write TH2 and TL2. As a baud rate generator, Timer 2 is

incremented every state time (fOSC/2) or asynchronously from pin

T2; under these conditions, a read or write of TH2 or TL2 may not

be accurate. The RCAP2 registers may be read, but should not be

written to, because a write might overlap a reload, and cause write

and/or reload errors. The timer should be turned off (clear TR2)

before accessing Timer 2 or RCAP2 registers.

Summary Of Baud Rate Equations: Timer 2 is in baud rate

generating mode. If Timer 2 is being clocked through pin T2(P1.0)

the baud rate is:

Baud Rate

+ Timer 2 Overflow Rate

If Timer 2 is being clocked internally, the baud rate is:

Baud Rate

OSC

[n *

[65536

(RCAP2H, RCAP2L)]]

* n =

16 in 6 clock mode

32 in 12 clock mode

Where fOSC = Oscillator Frequency

To obtain the reload value for RCAP2H and RCAP2L, the above

equation can be rewritten as:

RCAP2H, RCAP2L

+ 65536

OSC

Baud Rate

Timer/Counter 2 Set-up

Except for the baud rate generator mode, the values given for T2CON

do not include the setting of the TR2 bit. Therefore, bit TR2 must be

set, separately, to turn the timer on. See Table 11 for set-up of Timer 2

as a timer. Also see Table 12 for set-up of Timer 2 as a counter.

Table 11.

Timer 2 as a Timer

T2CON

MODE

INTERNAL CONTROL

(Note 1)

EXTERNAL CONTROL

(Note 2)

16-bit Auto-Reload

00H

08H

16-bit Capture

01H

09H

Baud rate generator receive and transmit same baud rate

34H

36H

Receive only

24H

26H

Transmit only

14H

16H

Table 12.

Timer 2 as a Counter

TMOD

MODE

INTERNAL CONTROL

(Note 1)

EXTERNAL CONTROL

(Note 2)

16-bit

02H

0AH

Auto-Reload

03H

0BH

NOTES:

1. Capture/reload occurs only on timer/counter overflow.

2. Capture/reload occurs on timer/counter overflow and a 1-to-0 transition on T2EX (P1.1) pin except when Timer 2 is used in the baud rate

generator mode.

P89C668 Datasheet(PDF) 39 Page - NXP Semiconductors

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