HD6475348R Datasheet, PDF (304/487 Pages) Hitachi Semiconductor – Single-Chip Microcomputer

15.3 CPU Interface
The A/D data registers (ADDRA to ADDRD) are 16-bit registers. The upper byte of each register
can be read directly, but the lower byte is accessed through an 8-bit temporary register (TEMP).
When the CPU or DTC reads the upper byte of an A/D data register, at the same time as the upper
byte is placed on the internal data bus, the lower byte is transferred to TEMP. When the lower
byte is accessed, the value in TEMP is placed on the internal data bus.
A program that requires all 10 bits of an A/D result should perform word access, or should read
first the upper byte, then the lower byte of the A/D data register. Either way, it is assured of
obtaining consistent data. Consistent data are not assured if the program reads the lower byte first.
A program that requires only 8-bit A/D accuracy should perform byte access to the upper byte of
the A/D data register. The value in TEMP can be left unread.
Figure 15-2 shows the data flow when the CPU (or DTC) reads an A/D data register.
< Upper byte read >
CPU
receives
data H'AA
Bus interface
Module data bus
TEMP
[H'40]
< Lower byte read >
CPU
receives
data H'40
Bus interface
ADDRn H
[H'AA]
ADDRn L
[H'40]
(n = A to D)
Module data bus
TEMP
[H'40]
ADDRn H
[H'AA]
ADDRn L
[H'40]
(n = A to D)
Figure 15-2 Read Access to A/D Data Register (When Register Contains H'AA40)
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