NEC mPD780065 Series Preliminary User's Manual page 244

(4) Synchronization control
Busy control and strobe control are functions to synchronize transmission/reception between the master
device and a slave device.
By using these functions, a shift in bits being transmitted or received can be detected.
(a) Busy control option
Busy control is a function to keep the serial transmission/reception by the master device waiting while
the busy signal output by a slave device to the master is active.
When using this busy control option, the following conditions must be satisfied.
• Bit 5 (ATE0) of the serial operating mode register 1 (CSIM1) is set to 1.
• Bit 1 (BUSY10) of the automatic data transmit/receive control register (ADTC0) is set to 1.
Figure 14-17 shows the system configuration of the master device and a slave device when the busy
control option is used.
Figure 14-17. System Configuration When Busy Control Option Is Used
The master device inputs the busy signal output by the slave device to the BUSY/P81 pin. The master
device samples the input busy signal in synchronization with the falling of the serial clock. Even if the
busy signal becomes active while 8-bit data is being transmitted or received, transmission/reception by
the master is not kept waiting. If 2 clocks after completion of transmission/reception of the 8-bit data,
the busy signal is active at the rising edge of the serial clock , the busy input becomes valid. Following
this, the master transmission/reception is kept waiting while the busy signal is active.
The active level of the busy signal is set by bit 0 (BUSY00) of ADTC0.
BUSY00 = 0: Active high
BUSY00 = 1: Active low
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CHAPTER 14 SERIAL INTERFACE (SIO1)
Master device
µ
( PD780065 Subseries)
SCK1
SO1
SI1
BUSY
Preliminary User's Manual U13420EJ2V0UM00
Slave device
SCK1
SI1
SO1