Monitor Operating System (MOS) of the Primer can be used to display results of the program at the LEDs in Hex or BCD by using appropriate routine calls from the monitor program. The primer is managed by the 8279 programmable interfacing device such as keyboard or display.
The seven-segment LEDs are connected to use the multiplexed technique. It cannot be directly accessed by writing subroutine services provided by the MOS.
Following points must be kept in mind:
- The MOS includes 36 service routines that the user can call by simply loading the service number in register C.
- The Primer Manual contains all the above available subroutines available for the user.
- For example, to display 96H in the accumulator at the user LED port in Hex byte stored in register E, we need to call service 1BH.
F001 3E MVI A, 96H F002 96 F003 5F MOV E, A F004 0E MVI C, 1BH F005 1B F006 CD CALL 1000H F007 00 F008 10 F009 FF RST 7
Following instructions can be modified as follows:
You need to enter the above codes at location F001H and then execute the code. The code will display the required 96H in the data field of the seven-segment display.
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