Operation In Asynchronous Mode - Hitachi H8/3035 Series Hardware Manual

Table 11-9 SMR and SCR Settings and SCI Clock Source Selection
SMR SCR Settings
Bit 7 Bit 1 Bit 0
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C/ CKE1 CKE0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

11.3.2 Operation in Asynchronous Mode

In asynchronous mode each transmitted or received character begins with a start bit and ends
with a stop bit. Serial communication is synchronized one character at a time.
The transmitting and receiving sections of the SCI are independent, so full-duplex
communication is possible. The transmitter and receiver are both double buffered, so data can be
written and read while transmitting and receiving are in progress, enabling continuous
transmitting and receiving.
Figure 11-2 shows the general format of asynchronous serial communication. In asynchronous
serial communication the communication line is normally held in the mark (high) state. The SCI
monitors the line and starts serial communication when the line goes to the space (low) state,
indicating a start bit. One serial character consists of a start bit (low), data (LSB first), parity bit
(high or low), and stop bit (high), in that order.
When receiving in asynchronous mode, the SCI synchronizes at the falling edge of the start bit.
The SCI samples each data bit on the eighth pulse of a clock with a frequency 16 times the bit
rate. Receive data is latched at the center of each bit.
Mode Clock Source
Asynchronous Internal
mode
External
Synchronous Internal
mode
External
SCK Pin Function
SCI does not use the SCK pin
Outputs a clock with frequency
matching the bit rate
Inputs a clock with frequency 16
times the bit rate
Outputs the serial clock
Inputs the serial clock
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