P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 34

• Manufacturer Part Number: P89V51RD2
• Description: 8-bit 80C51 5 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 12964
Product data
7.4.5 Summary of baud rate equations
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 is valid only if RCLK and/or TCLK =
T2CON register. Note that a rollover in TH2 does not set TF2, and will not generate
an interrupt. 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). 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. 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.
shows commonly used baud rates and how they can be obtained from Timer 2.
Timer 2 is in baud rate generating mode. If Timer 2 is being clocked through pin
T2(P1.0) the baud rate is:
If Timer 2 is being clocked internally, the baud rate is:
Where f
To obtain the reload value for RCAP2H and RCAP2L, the above equation can be
rewritten as:
Table 22:
----------------------------------------------------------------------------------------------- -
Baud rate
750K
19.2K
9.6K
4.8K
2.4K
600
16
Modes 1 and 3 Baud Rates =
Baud rate = Timer 2 overflow rate / 16
Baud rate = f
RCAP2H, RCAP2L = 65536
65536 RCAP2H RCAP2L
OscillatorFrequency
osc
Timer 2 generated commonly used baud rates
= oscillator frequency
–
osc
Rev. 01 — 01 March 2004
/ (16
Osc freq
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
(65536
f
osc
(RCAP2H, RCAP2L)))
/ (16
Timer 2
RCAP2H
FF
FF
FF
FF
FE
FB
baud rate)
8-bit microcontrollers with 80C51 core
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
P89V51RD2
RCAP2L
FF
D9
B2
64
C8
1E
Table 22
34 of 75
1
(3)
in