HD404849 Datasheet, PDF (81/125 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404849 Series
Pin Setting: The R2₁/SCK pin is controlled by writing data to serial mode register A (SMRA: $005). The
R2₂/SI and R2₃/SO pins are controlled by writing data to port mode register A (PMRA: $004). Refer to the
following Registers for Serial Interface section for details.
Transmit Clock Source Setting: The transmit clock source is set by writing data to serial mode register A
(SMRA: $005) and serial mode register B (SMRB: $028). Refer to the following Registers for Serial
Interface section for details.
Data Setting: Serial data is set by writing data to the serial data register (SRL: $006, SRU, $007).
Receive data is obtained by reading the contents of the serial data register. The serial data is shifted by the
transmit clock and is input from or output to an external system.
The output level of the SO pin remains unsettled until the first data is output after MCU reset, or until the
output level control in idle states is performed.
Transfer Control: The serial interface is activated by the STS instruction. The octal counter is reset to
000 by this instruction, and it increments at the rising edge of the transmit clock. When the eighth transmit
clock signal is input or when serial transmission/receive is discontinued, the octal counter is reset to 000,
the serial interrupt request flag (IFS: $023, bit 2) is set, and the transfer stops.
When the prescaler output is selected as the transmit clock, the transmit clock frequency is selected as 4t_cyc
to 8192t_cyc by setting bits 0 to 2 (SMRA0– SMRA2) of serial mode register A (SMRA: $005) and bit 0
(SMRB0) of serial mode register B (SMRB: $028) as listed in table 29.
Table 29 Serial Transmit Clock (Prescaler Output)
SMRB SMRA
Bit 0 Bit 2 Bit 1
0
0
0
1
1
0
1
0
0
1
1
0
Bit 0
0
1
0
1
0
1
0
1
0
1
0
1
Prescaler Division Ratio
÷ 2048
÷ 512
÷ 128
÷ 32
÷8
÷2
÷ 4096
÷ 1024
÷ 256
÷ 64
÷ 16
÷4
Transmit Clock Frequency
4096t_cyc
1024t_cyc
256t_cyc
64t_cyc
16t_cyc
4t _cyc
8192t_cyc
2048t_cyc
512t_cyc
128t_cyc
32t_cyc
8t _cyc
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