HT68F20 datasheet(21/210 Pages) HOLTEK

21 / 210 page

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60

Rev. 1.00

November 3, 2009

ing the ORG statement. The value at this ORG

statement is

²700H² which refers to the start address of

the last page within the 2K Program Memory of the

HT68F30. The table pointer is setup here to have an ini-

tial value of

²06H². This will ensure that the first data

read from the data table will be at the Program Memory

address

²706H² or 6 locations after the start of the last

page. Note that the value for the table pointer is refer-

enced to the first address of the present page if the

²TABRD [m]² instruction is being used. The high byte of

the table data which in this case is equal to zero will be

transferred to the TBLH register automatically when the

²TABRD [m]² instruction is executed.

Because the TBLH register is a read-only register and

cannot be restored, care should be taken to ensure its

protection if both the main routine and Interrupt Service

Routine use table read instructions. If using the table

read instructions, the Interrupt Service Routines may

change the value of the TBLH and subsequently cause

errors if used again by the main routine. As a rule it is

recommended that simultaneous use of the table read

instructions should be avoided. However, in situations

where simultaneous use cannot be avoided, the inter-

rupts should be disabled prior to the execution of any

main routine table-read instructions. Note that all table

related instructions require two instruction cycles to

complete their operation.

In Circuit Programming

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-circuit us-

ing a 5-pin interface. This provides manufacturers with

the possibility of manufacturing their circuit boards com-

plete with a programmed or un-programmed

microcontroller, and then programming or upgrading the

program at a later stage. This enables product manufac-

turers to easily keep their manufactured products sup-

plied with the latest program releases without removal

and re-insertion of the device.

MCU Programming

Pins

Function

PA0

Serial Data Input/Output

PA2

Serial Clock

RES

Device Reset

VDD

Power Supply

VSS

Ground

The Program Memory and EEPROM data memory can

both be programmed serially in-circuit using this 5-wire

interface. Data is downloaded and uploaded serially on

a single pin with an additional line for the clock. Two ad-

ditional lines are required for the power supply and one

line for the reset. The technical details regarding the

in-circuit programming of the devices are beyond the

scope of this document and will be supplied in supple-

mentary literature.

During the programming process the RES pin will be

held low by the programmer disabling the normal opera-

tion of the microcontroller and taking control of the PA0

and PA2 I/O pins for data and clock programming pur-

poses. The user must there take care to ensure that no

other outputs are connected to these two pins.

· Table Read Program Example

tempreg1 db

; temporary register #1

tempreg2 db

; temporary register #2

mov a,06h

; initialise low table pointer - note that this address

mov tblp,a

; is referenced

mov a,07h

; initialise high table pointer

tbhp,a

tabrd tempreg1

; transfers value in table referenced by table pointer data at program

; memory address

²706H² transferred to tempreg1 and TBLH

dec tblp

; reduce value of table pointer by one

tabrd tempreg2

; transfers value in table referenced by table pointer data at program

; memory address

²705H² transferred to tempreg2 and TBLH in this

; example the data

²1AH² is transferred to tempreg1 and data ²0FH² to

; register tempreg2

org 700h

; sets initial address of program memory

dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh

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