Holtek HT-IDE, User Manual

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clr LCM_CTRL.E ;low (trigger)
endif
ret
;== delay ==
delay: ;=delay for a while=
mov dtmp,a
drep:
sdz dtmp2 ;count down dtmp2
jmp drep
sdz dtmp ;count down dtmp
jmp drep
ret
end ;module
Program description
The program begins by calling in include files and by defining the LCM to
be on Port B. The LCM control lines are defined on Port C. External
modules are also declared to define whether the LCM is in 4-bit or 8-bit
mode.
The LCM will automatically conduct an internal reset during power-up.
However most program controlled LCMs will still utilize software for their
initialization. In this example the code begins at ’start’ by running some
initialization code. According to the data for the HD44780, there needs to
be at least 4.5 ms delay between each program. This is the function of the
LCM_DELAY code section. Before the LCM initialization has been carried
out it is not possible to check the status of BUSY. To issue instructions to
the LCM refer to the HD44780 instruction definitions. The code section
LCM.INC contains several often used instructions. Before the LCM writes
instructions it must first check whether LCM is in a busy condition. The
code section BUSY_CHK exists to check the BUSY status of the LCM. After
checking this, data can then be sent to the LCM. The ASCII codes to be
displayed should be placed in the last page of the program, and a table look
up method used to place the data in the accumulator, from where the code
section WRITE_CHAR can display it on the LCM.
Operation truth table of signal RS, R/W and E:
HT-IDE User’s Guide
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