Hi romario,

Interfacing to a 68000 is not easy. It would not be practical to try to teach you how to do it on a forum like this. The only thing I can suggest is try follow what they did with their 8255s, but just place them at different addresses. There may even be some unused address decodes you could use, but you'd have to dig through things yourself as not all the circuit is shown in that schematic. Obviously the 68K itself is not there and neither is the address decode circuitry.

 

Well what I am asking for are ideas especially connections of peripherals to the 8255 and not lessons on the 68000. I have two ADCs, 2 DACs, and 2 LCDs. One 8255 can accommodate two ADCs from Ports A and B operating in mode 0 while port C configured as control. Is it feasible to multiplex an LCD with either port A or port B? I intend to do the same with the other 8255. http://www.wantronix.de/pdf/decision/8255pci.pdf

 

When multiplexing I/O (even on an PPI 8255):
Decide which devices are the most to least important to process the input/output data.

Figure out which of the devices has enable pins. (Esp. true for reading devices; ADC in this case)

I recommend either changing the DAC chip or using a latch before it to hold the data stable. Other option is to disconnect the DAC output to prevent noise going to output.

Decide/state the interface to the LCD?
Number of Data bits and control lines?
Output only or bi-directional?
Edit: If standard LCD, I would suggest planning on 8bit data; but, only output/write to the LCD.

State all the chips numbers and input/output pins in a single post.
State the priority needed for all 6 devices.

Tim S.

 

1. The ZN448E ADC
8 output data bits
/BUSY
/READ
/WRITE
CK
2. The AD558 DAC
8 digital input data bits
/CS
/CE

3. The HD44780 LCD
8 data bits
RESET
R/W
Enable

 

Well what I am asking for are ideas especially connections of peripherals to the 8255 and not lessons on the 68000. I have two ADCs, 2 DACs, and 2 LCDs. One 8255 can accommodate two ADCs from Ports A and B operating in mode 0 while port C configured as control. Is it feasible to multiplex an LCD with either port A or port B? I intend to do the same with the other 8255. http://www.wantronix.de/pdf/decision/8255pci.pdf

Are you sure? I thought you wrote this:

This is where I am. I have got two more 8255 chips. How do I connect them to the 68000? There is a 50 pin bus extension socket is it possible I can connect the two 8255 chips to it?

Again, my answer would be:

The only thing I can suggest is try follow what they did with their 8255s, but just place them at different addresses. There may even be some unused address decodes you could use, but you'd have to dig through things yourself as not all the circuit is shown in that schematic. Obviously the 68K itself is not there and neither is the address decode circuitry.

To sum it up, without the entire schematic, how are we supposed to help you? How do we know what address the I/O are already on? Etc...

 

Well I have them but I was discouraged by posts that its difficult. I shelved that idea and instead tried to multiplex the chips I have. Someone suggested that I could connect 20 LCDs to two 8255. The circuit was uploaded on one of the posts.

 

1. The ZN448E ADC
8 output data bits
/BUSY
/READ
/WRITE
CK
2. The AD558 DAC
8 digital input data bits
/CS
/CE

3. The HD44780 LCD
8 data bits
RESET
R/W
Enable

I suggest finding out which ones are input/output.
As, I suggested in my past post.

Example, Is /BUSY in, out or bi-direction?

Note: since your past direction was from the external device you might as well keep it that way.

Tim S.

 

I seem to be getting somewhere with the hardware. Now I am stuck with software. I would like to initialise the 8255 PPI and read an analog to digital converter.

I need code to set the 8255 in BSR mode because I want to use port c as control and connect ADCs and DACs to A and B.

Port A is at address 00046000
Port B is at address 00046002
Port c is at address 00046004

 

Get a more recent platform to work on. I went from MC68Ks to Intel boxen in the mid-80's.

Today, I wouldn't dream of wasting my time on anything in that family of processors.