h8s-2161b Renesas Electronics Corporation., h8s-2161b Datasheet - Page 304

• Manufacturer Part Number: h8s-2161b
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

Section 10 14-Bit PWM Timer (PWMX)
10.4
DACNT, DADRA, and DADRB are 16-bit registers. The data bus linking the bus master and the
on-chip peripheral modules, however, is only 8 bits wide. When the bus master accesses these
registers, it therefore uses an 8-bit temporary register (TEMP).
These registers are written to and read from as follows.
Write: When the upper byte is written to, the upper-byte write data is stored in TEMP. Next,
when the lower byte is written to, the lower-byte write data and TEMP value are combined, and
the combined 16-bit value is written in the register.
Read: When the upper byte is read from, the upper-byte value is transferred to the CPU and the
lower-byte value is transferred to TEMP. Next, when the lower byte is read from, the lower-byte
value in TEMP is transferred to the CPU.
These registers should always be accessed 16 bits at a time with a MOV instruction, and the upper
byte should always be accessed before the lower byte. Correct data will not be transferred if only
the upper byte or only the lower byte is accessed. Also note that a bit manipulation instruction
cannot be used to access these registers.
Example 1: Write to DACNT
Example 2: Read DADRA
Table 10.2 Read and Write Access Methods for 16-Bit Registers
Register Name
DADRA and DADRB
DACNT
Legend:
Yes: Permitted type of access. Word access includes successive byte accesses to the upper byte
Rev. 3.00 Mar 21, 2006 page 250 of 788
REJ09B0300-0300
:
MOV.W R0, @DACNT
MOV.W @DADRA, R0
(first) and lower byte (second).
This type of access may give incorrect results.
Bus Master Interface
; Write R0 contents to DACNT
; Copy contents of DADRA to R0
Word
Yes
Yes
Read
Byte
Yes
Word
Yes
Yes
Write
Byte