ArduOne, the 8051 development board

Board description

ArduOne is an 8051 based development board equipped with a P89C51RD2HBA from NXP, formerly Philips. This microcontroller compared to the basic version has a total internal RAM memory of 1Kbyte and an additional internal counter capable of generating up to 5 PWM signals on as many output pins. The internal code flash memory is 64Kbyte wide and the device can be easily programmed through the serial port properly connected to a PC. The serial port serves both for programming and as a serial input/output port for the loaded program. All the input/output pins of the 4 ports (P0 .. P3) are directly connected to the side connectors of the board, while a 4-pin microswitch is used to set the microcontroller in programming mode or in execution mode. Arduone is programmable both in mnemonic assembly language, and using higher level languages. There are various compilers for different languages for ArduOne(and in general for the 8051 family of microprocessors). Among the most interesting that can be found on the internet there are; BASIC www.bipom.com/bascom51_down.php, Pascal turbo51.com or even Cobol www.keil.com/cobolad.pdf or PL / M www.bitsavers.org/pdf/intel/ISIS_II/121966-003_PLM-51_Users_Guide_Jan84.pdf There are also development environments available to program in C that also integrate a simulator to test the program before sending it to the microcontroller, also available on the net. In this website, however, we will only deal with programs written in C and in particular are going to use the free SDCC (Small Device C Compiler) compiler available and freely downloadable from sdcc.sourceforge.net. For a deeper understanding of the C language, a book is available in PDF format at the following link HERE, while for the C language implementation in SDCC a user guide is also available in the same SDCC page. I recomend you to read it to get the best from the sdcc compiler. As editor we are going to use TextPad, a relatively cheap editor that let you write in other programming languanges as well, and can embed, compilation and execution commands (SDCC for ArduOne excluded of course). For debugging there is also a simulator in the SDCC package named uCSim but I never tried it myself. I find much more convenient to directly activate the ArduOne serial port and use it for debugging, by sending or receiving from/to the terminal, messages in some breakpoint-like positions in the code. In this way, serial port becomes a kind of run time environment.

As you might see from the picture beside (trust me if you can't), ArduOne has a 11.0592 MHz Crystal clock. We this "strange" frequency because with that value the common baud rate frequencies are easily generated by the internal 8 bit counter. Any other crystal frequency can be used instead of that, providing that you change the counter settings to obtain usable baud rate. A good choice is 12MHz. With this frequency each instruction cycle by default is exactly 0.5 uS wide. When using machine code a precise time lapse can be calculated as multiple of this base being each machine instruction a multiple of this time period long. Depending on the internal settings, maximum crystal frequency can go up to 20MHz at 6 clock cycle/instruction or up to 33 MHz when the device is set to work with 12 cycles/instuction. Using the device default settings, using a 20MHz clock is like using 40MHz clock on a standard 8051 device.

Ports P1 and P3 have (see labels beside the left connector) alternative functions. For instance, P1 can be used as a whole 8 bit port or P1_0/T2 as external pulse source for the 16 bit counter 2, P1_1/T2EX can be used to control counter 2 or as additional interrupt signal source, P1_2/ECI can be used as external clock input for the 5 PWM signals and finally P1_3/PWM0 to P1_7/PWM4 can be used as 5 PWM source signals to control 5 analog loads as motors, lamps or any other power loads. P3 as well can be used as whole 8 bit port or interrupt source pins (P3_2/INT0 P3_3/INT1), input source for the two standard counters T0 and T1 (P3_4/T0 P3_5/T1). P3_0/TxD and P3_1/RxD are the pins used by the MAX232 level converter to communicate with the PC. By extracting the MAX232 from it's socket you can use these pins to connect directly your PC wirelessly using bluetooth both for programmin and as serial port, once connected a simple bluetooth interface to the board.

P0 and P2 are two additional 8 bit ports, their alternative function is to be used as interface for an optional external RAM up to 64Kbite wide. Since ArduOne does not use the control pin needed for this function (ALE (PSEN for ROM)) we will use these two ports as additional 8 bit ports. These two ports can be used directly as input port but if used as output ports a pull up resistor must be connected to each port pin.