h8s-2158 Renesas Electronics Corporation., h8s-2158 Datasheet - Page 332

• Manufacturer Part Number: h8s-2158
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

Section 11 14-Bit PWM Timer (PWMX)
11.4
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.
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 11.2 Read and Write Access Methods for 16-Bit Registers
Legend: Yes: Permitted type of access. Word access includes successive byte accesses to the
Rev. 3.00 Jan 25, 2006 page 280 of 872
REJ09B0286-0300
Register Name
DADRA and DADRB
DACNT
MOV.W R0, @DACNT
MOV.W @DADRA, R0
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.
Bus Master Interface
:
upper byte (first) and lower byte (second).
This type of access may give incorrect results.
; Write R0 contents to DACNT
; Copy contents of DADRA to R0
Word
Yes
Yes
Read
Byte
Yes
Word
Yes
Yes
Write
Byte