On Tue 29 Jul, Glen Fry wrote: > > Hi, > > I'm about to start designing a small system that is to provide reasonably > accurate temp control, drive a 2x16 or 2x20 lcd and handle12 inputs and 10 > outputs. > > I'm probably going to use a `74 for the job. > I'm looking to those of you that have experience with these these things for > advice. > > 1. I need to store temp setting and some other data in NV memory. I require > about 128 Bytes. May be written to once or twice a day. Can I use the EEProm > in the 74 for this? There is no EEPROM in the'74, so you'd have to use an external device (I2C preferred since it may share the bus with the ADC) > 2. I need a cheap but reliable 10 bit A/D with IIC. (dosen't every one?) Hmmm, I've been looking for I2C ADCs and have been unlucky so far. Instead I found the MAX186, which is 12 bits, with 8 channel MUX and internal 4.096V reference. Unfortunately, it requires 4 pins to drive it. > 3. Is it efficient to drive the LCD from the serial port or is 4 bits on a > parallel port the best way? Assuming that you know the speed of the PIC and the LCD, you don't even need a busy-feedback fromn the LCD. In that case, all you need is 6 I/O pins (four for data, one register select and one enable pulse), and some software delay loops to make sure you wait for the LCD to finish executing commands. You can find timings in the LCD controller datasheet, or simply test them yourself in the lab, and then (for the production run) *multiply all time constants by two* just to make sure that it continues to work over temperature variations. Frank ------------------------------------------------------------------------ Frank A. Vorstenbosch Phone: +44-181-636 3391 Electronics & Software Engineer or: +44-181-636 3000 Eidos Technologies Ltd., Wimbledon, London Mobile: +44-976-430 569