Hello people,


I'm using 89c668 which has 32 I/O ports.
2 are used for UART, 2 for I2C. So there's 28 general purpose I/O left.

My application needs more than available ports :
- 14 for graphic LCD (8 datas, 6 control)
- 3 for serial PLL (Enable, clock, data)
- 8 for matrix keyboard
- 6 digital outputs
- 2 digital input
- 2 for optical coder

Moreother my application may control an other peripheral but I've not yet the number of needed I/O
The timing for LCD have to be very short so it seems difficult to put it on I2C or other serial link.

I've to find an economic solution to extend the I/O.
Here are the solutions I've was thinking about :

1. Add 2 or 3 PCF8574 (8 bits I2C expander) for the digital I/O. However, I've to pool thru I2C very quickly to detect a change on an input or I have to use an interrupt. I could then remove the needed digital I/O and the keyboard.
The disadvantage is the PCF8574 cost.

2. I could use a streamed shift registers and to output the datas thru a software serial link. Idem for inputs

3. The last one would consist to use slave I2C microcontrollers and to transfer some processes into other micro (Keyboard, I/O, ...)

What do you think of this and what solution would you use. Maybe an other one ?

Thanks
Stephane