HD6417021 Hitachi Semiconductor, HD6417021 Datasheet - Page 398

• Manufacturer Part Number: HD6417021
• Description: SuperH RISC engine
• Manufacturer: Hitachi Semiconductor

In clocked synchronous serial communication, each data bit is output on the communication line
from one falling edge of the serial clock to the next. Data are guaranteed valid at the rising edge of
the serial clock. In each character, the serial data bits are transmitted in order from the LSB (first)
to the MSB (last). After output of the MSB, the communication line remains in the state of the
MSB. In the clocked synchronous mode, the SCI transmits or receives data by synchronizing with
the falling edge of the serial clock.
Communication Format: The data length is fixed at eight bits. No parity bit or multiprocessor bit
can be added.
Clock: An internal clock generated by the on-chip baud rate generator or an external clock input
from the SCK pin can be selected as the SCI transmit/receive clock. The clock source is selected
by the C/A bit in the serial mode register (SMR) and bits CKE1 and CKE0 in the serial control
register (SCR). See table 13.6.
When the SCI operates on an internal clock, it outputs the clock signal at the SCK pin. Eight clock
pulses are output per transmitted or received character. When the SCI is not transmitting or
receiving, the clock signal remains in the high state.
Figure 13.15 shows an example of SCI transmit operation. In transmitting serial data, the SCI
operates as follows.
1. The SCI monitors the TDRE bit in the SSR. When TDRE is cleared to 0 the SCI recognizes
2. After loading the data from the TDR into the TSR, the SCI sets the TDRE bit to 1 and starts
Serial clock
Note:
Serial data
that the transmit data register (TDR) contains new data, and loads this data from the TDR into
the transmit shift register (TSR).
transmitting. If the transmit-data-empty interrupt enable bit (TIE) in the SCR is set to 1, the
SCI requests a transmit-data-empty interrupt (TXI) at this time.
High except in continuous transmitting or receiving.
Figure 13.14 Data Format in Clocked Synchronous Communication
Transfer direction
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Bit 0
LSB
Bit 1
One unit (character or frame) of serial data
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
MSB
Bit 7
HITACHI 385
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