It is a modified version of the functional description from Willem.
The programmer consists of two parts that are completely separate: the serial section and the main part, the parallel EPROM section.
The serial section supports the I2C 24CXXX serie, 25C's and 93C's.
Microchip PIC's are also supported, they can be programmed with the I2C lines and Vpp. The great trick is the line DATA at the open collector Q6.
This section is a simple circuit that goes from D0(pin 2) to U1F, to Q6, Q5 U1D and to Busy (pin 11).
The serial circuit is also used to detect if the programmer is connected.
The parallel section consists of several parts:
The 2 4503's (tri-state buffer/driver) are used as a buffer for the 8 bit data(D0...D7) from the printerport, the 2 x 4 buffer is switched off for read mode and on for write mode( enable DA pin 1 U2 and U4). Read/write mode is controlled with autofeed(pin 14), this signal also switches address shift register data/clock inverted with U1E (enable DB pin 15 U2). As you can see D0(pin 2) and D1(pin 3) have a double function and must be switched off during write mode.
The 24 bit address register (3 x 4015, U6, U11, U14) is filled with the right address before every read or write byte action. D0 (clock) and D1 (data) are used for this purpose.
The 8 bit parallel to serial convertor shiftregister (4014) is used for reading 8 bit data. The parallel input (A ..H) is connected to the 8 bit eprom data bus (D0..D7). For every read action the right address will be clocked into the address register, the 4014 will be filled with PE high (pin 9) from D1 and a single puls from D2(inverted with U1C) to CLK (pin 10) PE will be set low and the bits are then clocked out with more pulses to CLK(pin 10), the read output goes via U1B to ACK (pin 10).Vpp is switched with Strobe (pin 1) and transistors Q3 and Q1.
Vcc is switched with Init (pin 16) and transistors Q4 and Q2.
The PGM or WE(write enable) pulse is controlled with Select (pin 17), the signal goes from printerport pin 17 to U4 pin 12, from U4 pin 11 to the DIP switches.
The DIP 12 switches are used to support different eprom types and packages. Vcc, Vpp and WE are switched to different program socket pins.
Information from the schema.
Usefull for furture processing.