Rev. 2.10
108
���� 02� 201�
Rev. 2.10
109
���� 02� 201�
HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
Programming Considerations
The TM Counter Registers and the Capture/Compare CCRAand CCRB registers, being either 10-bit
or 16-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.
Data
Bus
8-bit
Buffer
TMxDH
TMxDL
TMxBH
TMxBL
TMxAH
TMxAL
TM Counter Register (Read only)
TM CCRA Register (Read/Write)
TM CCRB Register (Read/Write)
As the CCRA and CCRB registers are implemented in the way shown in the following diagram and
accessing these register pairs is carried out in a specific way described above, it is recommended to
use the "MOV" instruction to access the CCRA and CCRB low byte registers, named TMxAL and
TMxBL, using the following access procedures. Accessing the CCRA or CCRB low byte registers
without following these access procedures will result in unpredictable values.
The following steps show the read and write procedures:
• Writing Data to CCRB or CCRA
♦
Step 1. Write data to Low Byte TMxAL or TMxBL
– note that here data is only written to the 8-bit buffer.
♦
Step 2. Write data to High Byte TMxAH or TMxBH
– 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 CCRB or CCRA
♦
Step 1. Read data from the High Byte TMxDH, TMxAH or TMxBH
– 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, TMxAL or TMxBL
– this step reads data from the 8-bit buffer.