Circuit programs Atmel AVR microcontrollers

Guo-Yin Xu, XuMicro, Houston, TX -- EDN, 3/30/2000

Atmel AVR µCs feature an enhanced RISC architecture that purportedly offer the highest MIPS-per-milliwatt capability in the 8-bit µC market. Figure 1 shows an easy-to-build AVR µC-programming circuit that can program the 40-pin AT90S4414/8515, the 20-pin AT90S1200/2313, and the eight-pin AT90S2323/2343. The programmer uses only three chips. It connects to the host PC's serial port via a MAX232 RS-232 transceiver, IC₁. Power comes from a 9V wall cube and the 78L05 linear regulator, VR₁. The AT89C4051 µC (IC₂) works with the 11.0592-MHz oscillator, and controls all programming tasks. LED₁ indicates the programmer's status. The circuit exploits the fact that all AVR µCs have a built-in SPI (serial-peripheral-interface) port that you can use to effect serial programming. The SPI port uses only the system-clock (SCK), master-output/slave-input (MOSI), and master-input/slave-output (MISO) pins. The AVR data book requires that, to place a µC in serial-programming mode, you must first pull the Reset and SCK pins low (Reference 1). Then, the µC must execute a programming-enable instruction before it can execute any program of erase instructions.

Hence, you need four pins to control the programming of a µC. For instance, the control signals from the AT89C4051 port pins P1.4 to P1.7 are for 40-pin µCs, the signals from P1.0 to P1.3 are for 20-pin µCs, and the signals from P3.2 to P3.5 are for eight-pin µCs. Note that you need pullup resistors for the AT89C4051 port pins P1.0 and P1.1, because these pins normally serve as analog-signal-input lines. Jumper JP₁ controls the 5V power supply for 20- and eight-pin µCs. You should remove the jumper when programming 40-pin µCs, which use a hard-wired connection to the 5V power. The circuit uses two 4-MHz ceramic resonators: CR₂ for 20-pin µCs, and CR/CR₃ for 40- or eight-pin µCs. Because the wires for the resonators should be as short as possible, the circuit uses no switching or jumping mechanisms. Instead, it uses one more resonator, CR₂ that's hard-wired to pins 4 and 5 of the 20-pin µC pins 14 and 15 of the ZIF socket. This connection does not disturb the programming of 40-pin µCs.

In addition to the hardware in Figure 1, the programmer also needs associated software. A binary file, AVRP1.BIN, holds the finished AVR-programmer software, burned into the AT89C4051 µC by using an 8X51 EPROM/flash µC programmer (Reference 2). A DOS file, AVRP1.EXE, contains the host-PC communication program. Click here to download these routines. (DI #2504)

REFERENCE

1."8-bit RISC Microcontrollers Data Book," Atmel Corp, August 1999.

2. Xu, Guo-Yin, "8X51 EPROM/flash microcontroller programmer," Circuit Cellar Magazine, April 1998.