sak-c868p-1rr Infineon Technologies Corporation, sak-c868p-1rr Datasheet - Page 237

• Manufacturer Part Number: sak-c868p-1rr
• Description: 8 - Bit Cmos Microcontroller
• Manufacturer: Infineon Technologies Corporation

9.2.1.1
By polling the receive port of the serial interface (P1.4/RxD Pin), the bootstrap loader
measures the low period of the test byte by using timer 2 as shown in
Figure 9-5
The time recorded is the receiving time of 8 bits (1 start bit plus 7 least significant bits of
the test byte). The resulting timer value is 16-bit (T2). This value is used to calculate the
8-bit reload value (RC2H,L) for Timer 2 as a baud rate generator.
The correlation between the baud rate (baud) and the reload value (RC2H,L) depends
on the internal MCU system frequency (fsys)
The relationship between the baud rate (baud) and the recording value of Timer 2 (T2)
depends on the MCU system frequency (fsys) and the number of received bits (Nb)
Combining
for RC2H,L leads to formula
The benefit of using the test byte 80H and recording 8 bits makes the formula easier for
realization in assembly language. The division with 64 can be simply achieved by a 6-
bit right shift operation. Additionally, the result of the division is rounded by a simple bit
comparison of the last right shifted bit. After setting Timer 2 to baudrate generator mode,
User’s Manual
RxD
Calculation of Timer 2 Reload Value
Equation [9.1]
Start Timer 2
Measuring the received time of a testbyte by using timer 2
RC2H,L = 2
baud =
Start
Bit
baud =
Timer 2 measures time for 8 bit cells
and
64 * (2
2
SMOD
f
16
12 * T2
SYS *
Equation
- T2*3/64
16
8 Data bits of test byte (80
* f
N
-RC2H,L)
b
SYS
[9.2], with SMOD=1 and Nb=8, resolving the
9-7
H
Stop Timer 2
)
The Bootstrap Loader
Figure
V 1.0, 2003-01
Stop
Bit
9-5.
C868
[9.1]
[9.2]
[9.3]