NEC PD75402A - Manual (Page 103)

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CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS
(b) To transmit/receive MSB-first data using an external clock (slave operation).
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➤
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P01/SCK
µ
PD75402A
SI
SO/SB0
SCK
SO
SI
Other Microcomputer
Main routine
MOV XA, #80H
MOV CSIM, XA ; Serial operation stopped, external clock specification
MOV XA, TDATA
MOV SIO, XA ; Transfer data setting & start of transfer
EI IECSI
EI
Interrupt routine
MOV XA, TDATA
XCH XA, SIO ; Receive data
÷
send data & start of transfer
MOV RDATA, XA ; Receive data save
RETI