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Philip Microprocessor P89C61 Flash Data Replication can be carried out by manipulate the baud rate generator, Usually, as a timer it would increment every machine cycle (i.e., 1/12 the oscillator frequency). As a baud rate generator, it increments every state time (i.e., 1/2 the oscillator frequency). Thus the baud rate formula is as follows:
Modes 1 and 3 Baud Rates = Oscillator Frequency
[32 × [65536 — (RCAP2H, RCAP2L)]]
Where: (RCAP2H, RCAP2L)= The content of RCAP2H and RCAP2L taken as a 16-bit unsigned integer.
The Timer 2 as a baud rate generator mode shown in below Figure, is valid only if RCLK and/or TCLK = 1 in T2CON register. Note that a rollover in TH2 does not set TF2, and will not generate an interrupt.

Timer 2 as a Timer

Thus, the Timer 2 interrupt does not have to be disabled when Timer 2 is in the baud rate generator mode. Also if the EXEN2 (T2 external enable flag) is set, a 1-to-0 transition in T2EX (Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but will not cause a reload from (RCAP2H, RCAP2L) to (TH2,TL2) after Philip Microprocessor P89C61 Flash Data Replication. Therefore when Timer 2 is in use as a baud rate generator, T2EX can be used as an additional external interrupt, if needed.

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 (osc/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 the Timer 2 or RCAP2 registers.

Table 5 shows commonly used baud rates and how they can be obtained from timer 2.

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

16

If Timer 2 is being clocked internally , the baud rate is:
Baud Rate = fOSC
[32 × [65536 — (RCAP2H, RCAP2L)]]
Where fOSC= Oscillator Frequency
To obtain the reload value for RCAP2H and RCAP2L, the above equation can be rewritten as:
= —( fOSC )

RCAP2H, RCAP2L

65536

32 × Baud Rate