Rev. 1.10
18
November 26, 2019
Rev. 1.10
19
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
In System Programming – ISP
The provision of Flash type Program Memory provides the user with a means of convenient and
easy upgrades and modifications to their programs on the same device.
As an additional convenience, Holtek has provided a means of programming the microcontroller
in-system using a two-line USB interface. This provides manufacturers with the possibility of
manufacturing their circuit boards complete with a programmed or un-programmed microcontroller,
and then programming or upgrading the program at a later stage. This enables product manufacturers
to easily keep their manufactured products supplied with the latest program releases without removal
and re-insertion of the device.
The Program Memory can be programmed serially in-system using the USB interface, namely using
the UDN and UDP pins. The power is supplied by the UBUS pin. The technical details regarding the
in-system programming of the devices are beyond the scope of this document and will be supplied
in supplementary literature. The Flash Program Memory Read/Write function is implemented using
a series of registers.
Flash Memory Read/Write Page Size
The Flash memory page size is 32 words. The page and buffer size are assigned as 32 words.
The following diagram illustrates the Read/Write page and buffer assignment. The write buffer is
controlled by the CLWB bit in the FRCR register. The CLWB bit can be set high to enable the Clear
Write Buffer procedure, as the procedure is finished, this bit will be cleared to low by hardware.
The Write Buffer is filled when the FWEN bit is set to high, when this bit is set high, the data in the
Write buffer will be written to the Flash ROM, the FWT bit is used to indicate the writing procedure.
Setting this bit high and check if the write procedure is finished, this bit will be cleared by hardware.
The Read Byte can be assigned by the address. The FDEN is used to enable the read function and
the FRD is used to indicate the reading procedure. When the reading procedure is finished, this bit
will be cleared by hardware.
Device
Page Size (Words)
Write Buffer (Words)
HT68FB240 (4K×16)
32
32