Rev. 1.10
64
November 26, 2019
Rev. 1.10
65
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
Programming Considerations
The TM Counter Registers and the Capture/Compare CCRA registers, being 10-bit, all have a low
and high byte structure. The high bytes can be directly accessed, but as the low bytes can only be
accessed via an internal 8-bit buffer, reading or writing to these register pairs must be carried out in
a specific way. The important point to note is that data transfer to and from the 8-bit buffer and its
related low byte only takes place when a write or read operation to its corresponding high byte is
executed.
As the CCRA register is implemented in the way shown in the following diagram and accessing
the register is carried out in a specific way described above, it is recommended to use the "MOV"
instruction to access the CCRA low byte register, named TMxAL, using the following access
procedures. Accessing the CCRA low byte register without following these access procedures will
result in unpredictable values.
The following steps show the read and write procedures:
•
Writing Data to CCRA
♦
Step 1. Write data to Low Byte TMxAL
– Note that here data is only written to the 8-bit buffer.
♦
Step 2. Write data to High Byte TMxAH
– Here data is written directly to the high byte registers and simultaneously data is latched
from the 8-bit buffer to the Low Byte registers.
•
Reading Data from the Counter Registers and CCRA
♦
Step 1. Read data from the High Byte TMxDH or TMxAH
– Here data is read directly from the High Byte registers and simultaneously data is latched
from the Low Byte register into the 8-bit buffer.
♦
Step 2. Read data from the Low Byte TMxDL or TMxAL
– This step reads data from the 8-bit buffer.
