HT66F25D View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT66F25D' PDF : 177 Pages View PDF
A/D Flash Type 8-bit MCU with EEPROM
HT66F24D/HT66F25D
Programming Considerations
The TM Counter Registers and the Capture/Compare CCRA and CCRB 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 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.
T� Counte� Registe� (Read only)
T�xDL TMxDH
8-bit
Buffe�
T�xAL TMxAH
T� CCRA Registe� (Read/W�ite)
T�xBL TMxBH
T� CCRB Registe� (Read/W�ite) Data
Bus
The following steps show the read and write procedures:
Writing Data to CCRB or CCRA
• Step 1. W rite data to Low Byte TMxAL or TMxBL - note that here data is only written to the 8-bit
buffer.
• Step 2. W rite 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.
Rev. 1.10
73
March 25, 2013
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