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Executing the program and checking result in 8085 Microprocessor
Here we will see how to use 8085 to write a program in 8085 kit. We will also see how to debug the program and check the result after successful execution.
Let us see a typical keypad structure of 8085 kit. (This keyboard pattern may vary in different kits of different manufacturers)
The following table will show the functionalities of different control keys. There are 16 alphanumeric keys (0-9, A-F) to provide data and address −
| Keys | Functionalities |
|---|---|
| RESET | Reset the system |
| VCT INT | Vector Interrupt. It generates hardware interrupt RST 7.5 via keypad |
| SHIFT | Provides second level commands to all keys |
| GO | Execute the program |
| SI | Execute in Single Step Mode |
| EXREG | Examine Register. It allows to see the values of different registers. |
| PRE | Point to previous memory address |
| DEL | Delete a part of program |
| INS | Insert a part of program |
| B.M | Block Move. This helps to move a block of memory to any RAM area |
| FILL | Fill some RAM area with constant values |
| REL | Reallocates the program written for some memory area. |
| INS DATA | Insert one or more data into memory |
| STRING | Find a string of data lying at particular address/s |
| MEMC | Compare two blocks of memory for equality |
Now we will see a sample program, where sixteen bytes of data are stored in memory locations at 8050H to 805FH. Transfer the entire block of data to new memory locations starting at 8070H.
Program
| T-States | Address | HEX Codes | Labels | Mnemonics | Comments |
|---|---|---|---|---|---|
| 10 | 8000 | 21, 50, 80 | START | LXI H, 8050H | Set up HL as a pointer for source memory |
| 10 | 8003 | 11, 70, 80 | LXI D, 8070H | Set DE for destination address | |
| 7 | 8006 | 06, 10 | MVI B,10H | Set up B to count 16 bytes | |
| 4 | 8008 | 7E | NEXT | MOV A,M | Get data byte from source memory |
| 7 | 8009 | 12 | STAX D | Store data byte at destination | |
| 6 | 800A | 23 | INX H | Pointing HL to next source location | |
| 6 | 800B | 13 | INX D | Pointing DE to next destination | |
| 4 | 800C | 05 | DCR B | Decrement count | |
| 10 | 800D | C2, 08, 80 | JNZ NEXT | If counter is not 0, go to transfer next byte | |
| 5 | 8010 | 76 | HLT | Stop | |
| | Total 17 bytes |
Total T-States = Toutside_loop + Tinside_loop
= (10+10+7+5) + ((4+7+6+6+4+10) x 16 - 3)
= 32 + (37 x 16 – 3)
= 32 + 589
= 621
The debugging options of 8085 kit.
| Command | Function/Format |
|---|---|
| Examine/Modify Memory | Displays/Modifies the contents of a memory location EXAM MEM <address> NEXT [[<data>] NEXT/PREV] EXEC |
| Examine/Modify register | Displays/modifies 8085 register contents. EXAM REG <reg key> [[<data>] NEXT]* EXEC |
| Single step | Executes a single user program instruction SINGLE STEP <start address> NEXT [[<start address>] NEXT]* EXEC |
| Go | Transfers control from monitor to user program GO <address> EXEC |
| Block move/Block copy | Moves/copies a block of data from one portion to another BLK MOVE <start address> NEXT <end address> NEXT <destination address> EXEC |
| Insert | Inserts one or more instructions in the user program INSERT [<low limit>] NEXT [<high limit>] NEXT <low insert address> NEXT <number of bytes> NEXT [[<data>] NEXT]* EXEC |
| Delete | Deletes one or more instructions in the user program DELETE [<low limit>] NEXT [<high limit>] NEXT <low delete address> NEXT <high delete address> EXEC |
Demonstration of block move operation
Initial Condition of memory addresses
| Source Address | Value | Destination Address | Value |
|---|---|---|---|
| 8000 | 00H | 8100 | XXH |
| 8001 | 11H | 8101 | XXH |
| 8002 | 22H | 8102 | XXH |
| 8003 | 33H | 8103 | XXH |
| 8004 | 44H | 8104 | XXH |
| 8005 | 55H | 8105 | XXH |
| 8006 | 66H | 8106 | XXH |
| 8007 | 77H | 8107 | XXH |
| 8008 | 88H | 8108 | XXH |
| 8009 | 99H | 8109 | XXH |
Keys:
<Block Move>, 8000H <Next>, 8009H <Next>, 8100H <Exec>
Final Condition of memory addresses
| Source Address | Value | Destination Address | Value |
|---|---|---|---|
| 8000 | 00H | 8100 | 00H |
| 8001 | 11H | 8101 | 11H |
| 8002 | 22H | 8102 | 22H |
| 8003 | 33H | 8103 | 33H |
| 8004 | 44H | 8104 | 44H |
| 8005 | 55H | 8105 | 55H |
| 8006 | 66H | 8106 | 66H |
| 8007 | 77H | 8107 | 77H |
| 8008 | 88H | 8108 | 88H |
| 8009 | 99H | 8109 | 99H |
Demonstration of block insert and block delete operations
Initial Condition of memory addresses
| Source Address | Value |
|---|---|
| 8000 | 00H |
| 8001 | 11H |
| 8002 | 22H |
| 8003 | 33H |
| 8004 | 44H |
| 8005 | 55H |
| 8006 | 66H |
| 8007 | 77H |
| 8008 | 88H |
| 8009 | 99H |
Keys:
<INSERT> 8000H <NEXT>, 8009H <NEXT>, 8005H <NEXT>, 5 <NEXT>, AAH <INSERT>, BBH <NEXT>, CCH <NEXT>, DDH <NEXT>, EEH <NEXT>
<DELETE>, 8000H <NEXT>, 800EH <NEXT>, 8005H <NEXT>, 8009H <EXEC>
Final Condition of memory addresses
| Source Address | Value |
|---|---|
| 8000 | 00H |
| 8001 | 11H |
| 8002 | 22H |
| 8003 | 33H |
| 8004 | 44H |
| 8005 | AAH |
| 8006 | BBH |
| 8007 | CCH |
| 8008 | DDH |
| 8009 | EEH |
| 800A | 55H |
| 800B | 66H |
| 800C | 77H |
| 800D | 88H |
| 800E | 99H |
Here we are using the 32K memory space 62256 at U3 with address map of 8000H to FFFFH. Instead of using HLT (76H) instruction to end the program we can use RST 5 (EFH) to return back to the monitor program. Because it helps us to debug whether a program has caused halt and hang or not.
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