• Register Read
When the CPU reads the upper byte, the upper byte of data is sent to the CPU and the lower byte
is placed in TEMP. When the CPU reads the lower byte, it receives the value in TEMP.
(As an exception, when the CPU reads OCRA or OCRB, it reads both the upper and lower bytes
directly, without using TEMP.)
Programs that access these registers should normally use word access. Equivalently, they may
access first the upper byte, then the lower byte by two consecutive byte accesses. Data will not be
transferred correctly if the bytes are accessed in reverse order, or if only one byte is accessed.
Coding Examples
To write the contents of general register R0 to OCRA:
MOV.W R0, @OCRA
To transfer the contents of ICRA to general register R0:
MOV.W @ICRA, R0
Figure 6-4 shows the data flow when the FRC is accessed. The other registers are accessed in the
same way.
Figure 6-4 (a). Write Access to FRC (when CPU Writes H'AA55)
Module data bus
(1) Upper byte write
Bus interface
CPU writes
data H'AA
FRC H
[ ]
FRC L
[ ]
TEMP
[H'AA]
(2) Lower byte write
Bus interface
Module data bus
CPU writes
data H'55
TEMP
[H'AA]
FRC H
[H'AA]
FRC L
[H'55]
129
Содержание H8/326 Series
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