Holtek HT-IDE, User Manual

Page: 201 / 258

jmp d3
ret
delays endp
org 300h ;TABLE
; RYG RYG
dc 0EBh ;1110 1011 G R
dc 0FBh ;1111 1011 O R
dc 0EBh ;1110 1011 G R
dc 0FBh ;1111 1011 O R
dc 0EBh ;1110 1011 G R
dc 0FBh ;1111 1011 O R
dc 0EBh ;1110 1011 G R
dc 0FBh ;1111 1011 O R
dc 0DBh ;1101 1011 Y R
dc 0BEh ;1011 1110 R G
dc 0BFh ;1011 1111 R O
dc 0BEh ;1011 1110 R G
dc 0BFh ;1011 1111 R O
dc 0BEh ;1011 1110 R G
dc 0BFh ;1011 1111 R O
dc 0BEh ;1011 1110 R G
dc 0BFh ;1011 1111 R O
dc 0BDh ;1011 1101 R Y
end
Program description
The program begins (1) by setting the value of the port control register to
determine which port bits are output and inputs. In this case each port bit
of port control register PAC is set to 0 as all bits in this port are used as
outputs. As the illuminated condition of the red, yellow and green lights is
fixed a table read instruction can be used to determine their values as
shown in section (2), however the values must first be setup. Because the
last page TABRDL instruction is used the table data is setup from address
300h. The highest address is 3FFh. In section (5) the table pointer is
incremented. In section (2) the display status of the LEDs is obtained from
the table, this value being placed on the output port as shown in (3). Due
to different timing delays being required for correct traffic light operation
several procedures exist within the program to provide different timings as
shown in (4) delayl, (7) delaym and (6) delays.
Chapter 15 Input/Output Applications
191