UPD784938 Datasheet, PDF (504/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
20.6.2 Master reception
If master reception is performed, it is necessary to give prior notice of “Slave transmission” to the unit set as slave.
Therefore, master reception requires at least two communication frames.
The slave unit prepares the transmission data, sets ENSLVTX (slave request transmission flag (bit 4 of the bus control
register (BCR)), and then waits.
Start
<1>
Broad-
casting
M address
P
S address
P
A
Control
Approx. 1,014µ s (mode 1)
PA
Telegraph
length
P
A
Data 1
Approx. 390 µs
(mode 1)
Data 1 P A Data 2 P A
Data n–1
PA
Data n
<2>
PA
n = Final number of data bytes
Initial preparation processing
Sets a unit address, slave address, and control data.
Communication start processing
Sets the bus control register (enables communication and master request).
<1> Interrupt (INTIE2) occurrence
Judgment of occurrence of error
↓
Judgment of slave request
↓
Judgment of collision result
→ Error processing
→ Slave processing
→ Remaster request processing
Interrupt (INTIE1) occurrence^{Note 1}
The receive data stored to the data register (DR) is read by macro service.
At this time, the data transfer direction is SFR (peripheral) → RAM (memory).
<2> Interrupt (INTIE2) occurrence
Judgment of occurrence of error →
↓
Judgment of end of communication →
↓
Judgment of end of frame
→
Error processing
End of communication processing
Re-communication processing^{Note 2}
Notes 1. If NACK is transmitted (hardware processing) in the data field, an interrupt (INTIE1) is not issued to
the CPU, but the same data is retransmitted from the slave.
If the receive data is not read in time until the next data is received, the hardware automatically transmits
NACK.
2. The vector interrupt processing in <2> judges whether the data has been correctly received within one
frame. If the data has not been correctly received (if the number of data to be received in one frame
could not be received), a request to retransmit the data must be made to the slave in the next
communication frame.
504
Preliminary User’s Manual U13987EJ1V0UM00