M38002M4 Datasheet, PDF (89/173 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.3 Serial I/O
Control procedure :
Control in the master unit
After a setting of the related registers is completed as shown in Figure 2.3.33, in the master unit
transmission or reception of 1-byte data is started simply by writing transmission data to the
Transmit buffer register.
To perform the communication in the timing shown in Figure 2.3.25, therefore, take the timing into
account and write transmission data. Read out the reception data when the Serial I/O transmit
interrupt request bit is set to “1,” or before the next transmission data is written to the Transmit
buffer register.
A processing example in the master unit using timer interrupts is shown below.
Interrupt processing routine
executed every 488 µs
CLT (Note 1)
CLD (Note 2)
Push register to stack
Note 1: When using the Index X mode flag (T).
Note 2: When using the Decimal mode flag (D).
q _{Push the register used in the interrupt}
processing routine into the stack.
N
Within a block transfer period?
Y
Read a reception data
q _{Generate a certain block interval by}
using a timer or other functions.
Count a block interval counter
q _{Check the block interval counter and}
determine to start of a block transfer.
Y
Complete to transfer a block?
N
Write a transmission data
N
Start a block transfer?
Y
Write the first transmission data
(first byte) in a block
Pop registers
q _{Pop registers which is pushed to stack.}
RTI
Fig. 2.3.27 Control in the master unit
3800 GROUP USER’S MANUAL
2-41