ST72F324BJ STMICROELECTRONICS [STMicroelectronics], ST72F324BJ Datasheet - Page 113

• Manufacturer Part Number: ST72F324BJ
• Description: 8-bit MCU, 3.8 to 5.5 V operating range with 8 to 32 Kbyte Flash/ROM, 10-bit ADC, 4 timers, SPI, SCI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72324B
Note:
Even parity
The parity bit is calculated to obtain an even number of ‘1’s inside the frame made of the 7 or
8 LSB bits (depending on whether M is equal to 0 or 1) and the parity bit, for example,
data = 00110101; 4 bits set => Parity bit will be 0 if Even parity is selected (PS bit = 0).
Odd parity
The parity bit is calculated to obtain an odd number of ‘1’s inside the frame made of the 7 or
8 LSB bits (depending on whether M is equal to 0 or 1) and the parity bit, for example,
data = 00110101; 4 bits set => Parity bit will be 1 if Odd parity is selected (PS bit = 1).
Transmission mode
If the PCE bit is set then the MSB bit of the data written in the data register is not transmitted
but is changed by the parity bit.
Reception mode
If the PCE bit is set then the interface checks if the received data byte has an even number
of ‘1’s if even parity is selected (PS = 0) or an odd number of ‘1’s if odd parity is selected
(PS = 1). If the parity check fails, the PE flag is set in the SCISR register and an interrupt is
generated if PIE is set in the SCICR1 register.
SCI clock tolerance
During reception, each bit is sampled 16 times. The majority of the 8th, 9th and 10th
samples is considered as the bit value. For a valid bit detection, all the three samples should
have the same value otherwise the noise flag (NF) is set. For example: If the 8th, 9th and
10th samples are 0, 1 and 1 respectively, then the bit value will be ‘1’, but the Noise flag bit
is set because the three samples values are not the same.
Consequently, the bit length must be long enough so that the 8th, 9th and 10th samples
have the desired bit value. This means the clock frequency should not vary more than 6/16
(37.5%) within one bit. The sampling clock is resynchronized at each start bit, so that when
receiving 10 bits (one start bit, 1 data byte, 1 stop bit), the clock deviation must not exceed
3.75%.
The internal sampling clock of the microcontroller samples the pin value on every falling
edge. Therefore, the internal sampling clock and the time the application expects the
sampling to take place may be out of sync. For example: If the baud rate is 15.625 kbaud (bit
length is 64µs), then the 8th, 9th and 10th samples will be at 28µs, 32µs and 36µs
respectively (the first sample starting ideally at 0µs). But if the falling edge of the internal
clock occurs just before the pin value changes, the samples would then be out of sync by
~4µs. This means the entire bit length must be at least 40µs (36µs for the 10th sample + 4µs
for synchronization with the internal sampling clock).
On-chip peripherals
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