3-Wire Serial I/O Mode - NEC 78K0 User Manual

17.4.2 3-wire serial I/O mode

The one-byte data transmission/reception is executed in the mode in which bit 6 (ATE0) of serial operation mode
specification register 0 (CSIMA0) is cleared to 0.
The 3-wire serial I/O mode is useful for connecting peripheral ICs and display controllers with a clocked serial
interface.
In this mode, communication is executed by using three lines: serial clock (SCKA0), serial output (SOA0), and
serial input (SIA0) lines.
(1) Registers used
• Serial operation mode specification register 0 (CSIMA0)
• Serial status register 0 (CSIS0)
• Divisor selection register 0 (BRGCA0)
• Port mode register 14 (PM14)
• Port register 14 (P14)
Notes 1. Bits 7, 6, and 4 to 1 (CSIAE0, ATE0, MASTER0, TXEA0, RXEA0, and DIR0) are used. Setting of
bit 5 (ATM0) is invalid.
2. Only bit 0 (TSF0) is used.
The basic procedure of setting an operation in the 3-wire serial I/O mode is as follows.
<1> Set the BRGCA0 register (see Figure 17-6)
<2> Set bits 4 to 1 (MASTER0, TXEA0, RXEA0, and DIR0) of the CSIMA0 register (see Figure 17-3).
<3> Set bit 7 (CSIAE0) of the CSIMA0 register to 1 and clear bit 6 (ATE0) to 0.
<4> Write data to serial I/O shift register 0 (SIOA0). → Data transmission/reception is started
Notes 1. This register does not have to be set when the slave mode is specified (MASTER0 = 0).
2. Write dummy data to SIOA0 only for reception.
Caution Take relationship with the other party of communication when setting the port mode
register and port register.
CHAPTER 17 SERIAL INTERFACE CSIA0
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