Amicroprocessor learning board having built-in monitor program is the thebest way to study the architecture of a given microprocessor. While runninga monitor program, we can practice enter a machine code in hexadecimalnumber and let the cpu executes it. We can examine memory, cpu registersand I/O pin. This led me to design a learning board for 89C52 cpu, theC52EVB. The C52EVBhas been designed for study Assembly and C language programming at theDepartment of Applied Physics, KMITL since 1999. One day I brought an I2Cserial eeprom, 24LC256, 32kB! The chip maker said we can get erase/writecycle minimum at 1,000,000 cycles! and the retention time is about 40Yrs!So I got the idea to use the eeprom for program saving and booting whenpowerup. The EXTRA memory space of PAULMON2 monitor program enables meto put the eeprom ZAP functions. I designed the new version of C52EVB toprovide such eeprom ZAP functions. Under program development, student willhave 32KB for program testing. After the program works fine, they can savethe binary image into eeprom with maximum 32KB! I put the eeprom bootingas a startup code in PAULMON2, so when power up the board, after serialport initialized, the booting function will check a jumper if it set, itwill read the binary image from eeprom, write to SRAM and jump to startaddress running the program.
Figure 1: Block diagram of C52EVB V2.0
The new C52EVB V2.0 features;
- CPU: 89C52, CMOS 8-bit microcomputer @11.0592MHz,
- MEMORY: 62256, 32KB SRAM for both code and dataspace,
- EEPROM: 24LC256, 32KB serial eeprom,
- I/O pins: P1,P3 of 89C52, 24-bit I/O pins using8255 PPI,
- Debug LED: single dot LED connected to P1.7,
- RS232 Level Converter: MAX232,
- Serial Interface: 9600 8n1,
- Monitor Program: 8KB PAULMON2 including external eeprom boot loader,
- I/O Connectors: four 16-pin connectors with modular design to provideI/O adapter board to be stacked,
- Programming: hexadecimal machine code, ASM51 Cross assembler, 8051Micro-C compiler with small memory model.
Circuit
Here is the complete schematic C52evbv2.pdf.(Note. the latest schematic is in the C52EVB Reference Manual).
The circuit for CPU, memory and decoder is the same as C52-EVB. I added8255 chip to provide 24-bit I/O pins. The 8255 chip was put in the externaldata memory space by using A15 address line to enable it. The address of8255 registers are mapped into external data memory as follows;
| PORTA = 0x0000, PORTB = 0x0001, PORTC = 0x0002 and Control Register = 0x0003. |
So to talk to these registers, we must use MOVX instruction, e.g. towrite control register for all output mode, the control word is 0x80.
| MOV A,#80H MOV DPTR,#0003 MOVX @DPTR,A |
With Micro-C we may use function poke(unsigned address, int value);
| poke(0x0003,0x80); // or with pointer, unsigned char *dptr; // declare pointer vairable,dptr, not the same as DPTR register in cpu dptr = 0x0003; // set dptr to 0x0003 |
For RS232C level converter, I changed from DS275 to MAX232. The DB9is male type. The signal ties to DB9 connector is for NULL MODEM cable.The cable has a cross signal between TxD and RxD.
A big change is the I2C serial eeprom interfacing. It uses twoI/O pins, i.e. P3.4 for SDA, data line and P1.0 for SCL, shift clock. The24LC256 is 32kB eeprom. The address space is range from 0x0000 to 0x7FFF.
Software
mypaulm3.hex is the intel hex filefor 89C52 chip. It includes EEPROM ZAP functions. You may use Easy-DownloaderV2.0 to program the this file into a 89C52 chip.
Here is the source code that I modified;
The 1st 4kB or the hex code of mypaulm2.asm is mostly the same as myfirst design. The 2nd 4kB, however is the place where I put extra commandwith the help of PAULMON2's Program Header technique. You may study thesource code of myextra.asm to see how I put the service functions for eeprom.The current version of mypaulmon3.hex is left space for another purposeonly less than 200 Bytes. So if need to put more command, some of monitorcommand may need to delete. Above files need AS31 Assembler to convertfrom assembly code to object file. It may get from originalPUALMON2website.
Using ZAP eeprom functions
Let me talk a bit about how to use the external eeprom booting. Withouta jumper ties P3.5 to GND signal, i.e. monitor mode. When press help commandwith ? we get;
| PAULMON2 Loc:8000 > Help Standard Commands PAULMON2 Loc:8000 > |
The ZAP EEPROM is user installed command.
Try Z command,
| PAULMON2 Loc:8000 > ZAP EEPROM 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD |
The eeprom functions have three commands;
1 SAVE save start addess,number of byte and binary image to eeprom
2 DUMP dump hex code on screen
3 LOAD load binary image to SRAM,and execute at start address in SRAM
We can use number 1, 2, or 3 to execute the command. To quit from ZAPeeprom, just press SPACE BAR, say.
Since the SAVE function needs two input values; start address and numberof byte to be saved, so suppose the program was tested and worked fine,quit from ZAP eeprom with SPACE BAR pressed, then use DOWNLOAD command.
| 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD > PAULMON2 Loc:8000 > Download Begin ascii transfer of Intel hex file, or ESC to abort SEnding file C:HELLO.HEX Summary: PAULMON2 Loc:8000 > |
We see that PUALMON2 tells the number of byte that received. We maythen use this number for SAVE function. Now get back to Z command and press1 followed with start address and number of byte.
| Download completed Summary: PAULMON2 Loc:8000 > ZAP EEPROM 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD |
You may wonder why the counting number was so big. I used 2's complementor negative number for counting. It is easy to use INC DPTR and check bothDPH and DPL are zero for looping (detail of assembly code is in myextra.asm).When completed, it will show Done...
Let DUMP it, what's in eeprom now. The physical address of SRAM is 0x8000-0xFFFF.Whereas the physical address of eeprom is 0x0000-0x7FFF. So when we dumpthe content of eeprom we can start with address 0x0000. Take a look moredetail in the address 0x0000-0x000F, or first 16 bytes.0080 is start address of binary image in SRAM or 0x8000. The byteorder is from low order byte to high order byte. Similarly for A8FC , is 2's complemment of 856 or 0xFCA8.Iprovided this 16 bytes for record information. The rest is available forother parameters, if needed.
From address 0x0010 is start of binary image thatread from SRAM start address.The hex code of these three bytes, i.e. 0280 11is LJMP 0x8011 instruction.
| 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD > eeprom address [0000-7FFF] > 0000 0000 00 80 A8FC 4D 02 20 52 00 00 00 A6 93 01 00 00 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD |
Let try press LOAD command with key '3', see what happen;
| 24LC256 EEPROM functions 1 SAVE, 2 DUMP, 3 LOAD > Loading... hello world 1 1 1 hello world 2 2 10 hello world 3 3 11 hello world 4 4 100 hello world 5 5 101 hello world 6 6 110 hello world 7 7 111 hello world 8 8 1000 hello world 9 9 1001 hello world 10 A 1010 hello world 11 B 1011 hello world 12 C 1100 hello world 13 D 1101 |
The binary image will be loaded from eeprom and written to SRAM. Whencomplete the cpu started to run.
Now try turn off power, and put a jumper ties P3.5 to GND. Turn boardpower on again, we get;
| Loading... hello world 1 1 1 hello world 2 2 10 hello world 3 3 11 hello world 4 4 100 hello world 5 5 101 hello world 6 6 110 hello world 7 7 111 hello world 8 8 1000 hello world 9 9 1001 hello world 10 A 1010 hello world 11 B 1011 hello world 12 C 1100 hello world 13 D 1101 hello world 14 E 1110 |
As long as the jumper makes P3.5 to logic '0', when startup, after initializeserial port with 9600 8n1, the binary image will be loaded into SRAM andwill be executed automatically.
Here is a sample of jumper that enables boot loader when powerup.
To get back to monitor mode is then easily be made by take the jumperout, makes P3.5 to logic '1'.
Download
| Schematic | C52evbv2.pdf |
| Assembly Source code | mypaulm2.asm myextra.asm |
| Intel Hex files | mypaulm2.hex myextra.hex |
| Intel Hex file (combines above two files) | mypaulm3.hex |
C52EVB V2.0 Reference Manual | C52reference.pdf (1,076,546Bytes) |
| PCB gerber files( see below new gerber file) | C52gerber.zip (185KB) |
| OrCAD 9.1 MAX file (see below new MAX file) | C52V2-1.max (325KB) |
| OrCAD 9.1 Schematic Capture file | C52V2.DSN (112KB) |
| OrCAD 9.1 Netlist file | C52V2.MNL (44KB) |
| C52EVB V2.0 BOM | c52evbv2.bom |
Sample Picture of PCB
Errata
- 20 August 2002: pin designation silk-screen at J4.I placed a wrong position of the text label between P1.1 and P1.2 on PCB.There is no error in schematic and reference manual.
Updated gerber and MAX files
- 23 September 2002: new gerber file that correctsabove errata and provides bigger mounting hole. Click here to download C52EVB2-2gerber.zip (202KB), andC52EVB2-2.max (330KB).
Contribution to C52EVB
- C52evb1.zipSingle side layout of C52EVB V2.0 made by Vu Nhu Khanh from Vietnam.
- PCB2.PCBProtel PCB file for C52EVB version1 made by Winston Amorim from Brazil.
