User manual

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CHAPTER 5 PERIPHERAL HARDWARE FUNCTIONS

(10) Transfer start

Serial transfer is started by writing transfer data in shift register (SIO), provided that the following two

conditions are satisfied:

• The serial interface operation enable/disable bit (CSIE) is set to 1.

• The internal serial clock is not operating after 8-bit serial transfer, or SCK is high.

Cautions 1. Transfer cannot be started by setting CSIE to 1 after writing data to the shift

2. The N-ch transistor needs to be turned off when data is received. So FFH must

be written to SIO beforehand. However, when the wake-up function specification

bit (WUP) is set to 1, the N-ch transistor is always off. So FFH need not be

written to SIO beforehand for reception.

3. If data is written to SIO when the slave is busy, the data is not lost. Transfer is

started when the busy state is released and input to SB0 (or SB1) goes high.

When eight bits have been transferred, serial transfer automatically terminates setting the interrupt request

flag (IRQCSI).

Example When RAM data specified by the HL register is transferred to SIO, from which data is loaded

into the accumulator at the same time, and serial transfer is started.

MOV XA,@HL ; Extracts transmit data from RAM

SEL MB15 ; or CLR1 MBE

XCH XA,SIO ; Exchanges transmit data with receive data and startstransfer

(11) Notes on the SBI mode

(a) Whether a slave is selected is determined by detecting a match for a slave address received after

bus release (in the state of RELD = 1).

An address match is detected usually using, an address match interrupt (IRQCSI) generated when

WUP is 1. So detect selection/nonselection state by slave address when WUP is set to 1.

(b) When determining whether a slave is selected without using an interrupt when WUP = 0, do not use

the address match detection method. Instead, use transfer of commands set in advance in a program.

of BUSY is directed, the BUSY signal is output until the next falling edge of the serial clock (SCK)

appears. Before setting WUP to 1, be sure to confirm that the SB0 (or SB1) pin is high after releasing

BUSY.