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Trouble CFAG240128L-TMI-TZ-TS

Ben37

New member
Hi,
We are trying to use a CFAG240128L-TMI-TZ-TS screen for a school project. Unfortunatly, it still dosent work after a 2 weeks. Here is our trouble:

When we do a StatusCheck, STA1 is always Low. It mean that the read/write Capability is never Enable.
Here is the state of our data lines:

Read = 0 (Active)
Write = 1 (Unactive)
ChipEnable = 0 (Active)
Command/Data = 1 (Command is Active)

On the data bus we can see the Status word but STA1 is never high so we can't send any commands.
The controller on this screen is a T6963C. We are using a DS89C450 but the timmings are enough slow for the screen.
We will still work on it but any answer would be very appreciate
Thanks for helping us.

Students
PS: sorry for our english it is not our born language :)
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Are all bits of the status word always low, or only the STA1? Are you sure that your code is changing the data bus port to inputs while trying to read status?
 

Ben37

New member
The rest of the status word is on the databus and the databus is bidirectional (from the DS89C450 datasheet). The trouble is only on this bit (STA1)
Thanks for helping!

Students
 
I am not sure that you have answered my questions.
The rest of the status word is on the databus...
Does that mean that all other status bits can be read as '1' state, but only STA1 does not go to '1' state?

Yes, the data bus is bidirectional according to the data sheet. But which port number are you using for the data bus? Are you setting the port to all 1's when you are trying to read status?
 

Ben37

New member
Sorry if it wasent enough clear.

No, not all of the others Status word bits are "1". Some of them must be at "0". We don't have any trouble with the others bits but only with the second one (STA1). He won't be at "1" and is always low...

We are using Port0 as DataBus/AdressBus (we latch the adress when needed). This screen only need the DataBus. We try to read the Status Word. To do this, we put Read to Low, Write to High, C/D to High and ChipEnable Low.

From the datasheet, this should sent the StatusWord on the DataBus and it does. But STA1 is always low and mean that the read/write Capability is never Enable.

"Are you setting the port to all 1's when you are trying to read status?"

Im not sure what you mean by this. We don't have to put Port0 to input or output on the DS89C450.

Thanks for helping again!!
 
"Are you setting the port to all 1's when you are trying to read status?"

Im not sure what you mean by this. We don't have to put Port0 to input or output on the DS89C450.
According to the data sheet, port0 is open drain (no pullup resistors). So when you want to read the port as inputs, you must turn off the output transistors by writing all '1's to the port, else the output transistors will hold the port pins at ground=0 volts. The data sheet says "Pullup resistors are required only when using port 0 as an I/O port".

You should try pullup resistors on STA0 and STA1. Try 10K ohms to see if it makes any difference.

Or maybe I am making the mistake, and you are treating the display as if it is external memory on the bus, and not using port0 as "I/O". If so, that is unusual, and maybe the timing is still too fast during the read state, and the data bit is not going high soon enough.

Have you tried using an oscilloscope to see if the timing is slow enough? The display access time is 150 nS for reading, so maybe your RD pulse is too short.

You could also try using a different port for the data bus, and another port to control the RD, RW, CE, C/D lines, and do all the I/O necessary to make the control pulses. That is the usual way that these displays are interfaced.
 

Ben37

New member
First, thanks for these quick answer!

I will try them tomorow at school. Also, we always use Oscilloscope to see our signals. The timmings are good. May be the pullups i will try Resistors and the wintest programs.
I will give you answer tomorow!
Thanks!

Student
 

Ben37

New member
i got some news!
we tried something else: we are not using any uC anymore, just for the tests of the screen.

CE is low, C/D is high, we send some RD signals and check the databus. But nothing is moving. All the data lines are low (0v). It look like the screen won't answer the StatusWord....
anybody know why?

Thx again for helping!
 

Ben37

New member
Also, we tried the Wintest software but it is not working... Some lines appears on the screen but it is Random
 
CE is low, C/D is high, we send some RD signals and check the databus. But nothing is moving. All the data lines are low (0v). It look like the screen won't answer the StatusWord....
anybody know why?
What is the state of the RESET input (pin 10)? Is the WR input high while you try this?
Also, we tried the Wintest software but it is not working... Some lines appears on the screen but it is Random
The Wintest program does not control the RESET pin, so how did you connect it?

I do not have enough information from you to suggest any other things to try.
 

Ben37

New member
Everything is now working, thx everyone for your help!
The screen is broken. We tried with another one and it is working.

Thanks!!
 
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