VPP control

During programming, the VPP is applied to the device through the U3. The TX line from the PC switches on the U3 and the VPP voltage is applied to the device through 100 ohms resistor R3.

PGD and PGC lines

The RTS and DTR lines are the PGD and PGC. The RX line is for data readback. Diodes D1, D2 D3 and D4 clamp the RS232 voltages to +5 volts and ground.

ICSP connections

A 5 pins connector (J3) is needed to interface the programmer to the target board for In Circuit Serial Programming (ICSP). The pin functions are as follows.

Pin 1 . VPP = 13.5 volts (12.5 volts would be ideal for many devices)
Pin 2 . VCC = 5 volts
Pin 3 . PGD = Programming data
Pin 4 . PGC = Programming clock
Pin 5 . GND = 0 volts

In this stand alone programmer circuit, all connections are made to the 40 pins ZIF socket. This will be for a stand alone programmer. Some of the pins in the ZIF socket are wired to ground, VCC, VPP, PGD and PGC. This is to support 8 pins to 40 pins programming. The device placement justification is shown in the dotted lines.

For 28 and 40 pins device, short J2 1 and 2 and short J2 2 and 3 for the other devices by a SPDT toggle switch or burg pins. 28 and 40 pins device are top justified. The 18 pins devices are bottom justified. The 8, 14 and 20 pins devices are justified to pin 3 (Pin 1 of the device to be placed at pin 3 of the ZIF socket).

The 5 pins for ICSP can be burgpins or a reliamate connector at the end of a 6" cable.