| Author |
Message |
slodgey
Guest
|
 Posted:
Sun Nov 06, 2005 12:48 am Post subject:
PLD Help wanted! |
|
|
Hi All, I have recently seen a PCB that uses a GAL16V8 to control a 4x7
keyboard matrix. The company that made the PCB no longer exist and the
GAL is dead! It appears to me that the terminals 17-19 are used to
address the row and then read back the column.
I have no schematic for this PCB but this is how its been reversed
engineered.
Row 0-4 are on pins 13-16
Col 0-6 are on pins 2-8
Write pin 1
Read pin 9
D0-D2 are on pins 17-19
Keypad Interupt Pin 12
I have only ever used a PLD to do simple addressing and never used the
pins to be bi-directional. Can anyone help in showing me how this can
be achieved?
Many thanks
|
|
| Back to top |
|
 |
petrus bitbyter
Guest
|
| Posted:
Sun Nov 06, 2005 1:35 am Post subject:
Re: PLD Help wanted! |
|
|
"slodgey" <slodge1313@aol.com> schreef in bericht
news:1131216507.072084.205020@g43g2000cwa.googlegroups.com...
| Quote: | Hi All, I have recently seen a PCB that uses a GAL16V8 to control a 4x7
keyboard matrix. The company that made the PCB no longer exist and the
GAL is dead! It appears to me that the terminals 17-19 are used to
address the row and then read back the column.
I have no schematic for this PCB but this is how its been reversed
engineered.
Row 0-4 are on pins 13-16
Col 0-6 are on pins 2-8
Write pin 1
Read pin 9
D0-D2 are on pins 17-19
Keypad Interupt Pin 12
I have only ever used a PLD to do simple addressing and never used the
pins to be bi-directional. Can anyone help in showing me how this can
be achieved?
Many thanks
|
That's not too difficult. The "output" cells have a product term that
controls the output. When activated, the corresponding output driver goes
tri-state but the internal feedback stays active. This way the pin can be
used for input. So the read pin (9) is used to keep D0-D2 (17-19) tristate,
then a pulse on write (1) is used to clock the (decoded) addresses into the
output cells (13-16) of the rows. Now the outputs of the component that
provided the row address are made tristate, then the read pin (9) is used to
release the tristate of the D0-D2 (17-19), at the same time putting the
encoded column on them.
So D0-D2 is a real bidirectional databus.
As for the interrupt, I guess it is activated when, after a write, the
column appears to be nonzero.
petrus bitbyter |
|
| Back to top |
|
|
slodgey
Guest
|
| Posted:
Sun Nov 06, 2005 1:35 am Post subject:
Re: PLD Help wanted! |
|
|
Many thanks, I'll give it a go!
|
|
| Back to top |
|
|
slodgey
Guest
|
| Posted:
Thu Nov 10, 2005 1:35 am Post subject:
Re: PLD Help wanted! |
|
|
I still need help!
After trying, I now get an error of Invalid input pin 19. How do I
define these pins D0-D2 (17-19). Can anyone give me an example piece of
code to show me how to use these pins as bi-directional I/O.
Many thanks |
|
| Back to top |
|
|
petrus bitbyter
Guest
|
| Posted:
Fri Nov 11, 2005 1:19 am Post subject:
Re: PLD Help wanted! |
|
|
"slodgey" <slodge1313@aol.com> schreef in bericht
news:1131578069.659468.187950@z14g2000cwz.googlegroups.com...
| Quote: | I still need help!
After trying, I now get an error of Invalid input pin 19. How do I
define these pins D0-D2 (17-19). Can anyone give me an example piece of
code to show me how to use these pins as bi-directional I/O.
Many thanks
|
What tool do you use? FAIK there is no need to specify the outputs for I/O.
You simply set the other outputs according to the value that appears on
these output pins (D0-D2). The older tools I'm aware of do not bother
whether that value comes from the output cells (when activated) or from the
bus (when the outputs are in tristate). Maybe newer tools like VHDL do check
this situation as they need it for simulation.
(Even then, I like a warning rather then an error report. Of couse you are
forced to specify correctly this way but I hate to be forced.)
Can you write (a part of) the code you've written along with the tool you
used for it?
petrus bitbyter |
|
| Back to top |
|
|
slodgey
Guest
|
| Posted:
Wed Nov 16, 2005 5:35 pm Post subject:
Re: PLD Help wanted! |
|
|
The Tool I use is for ATMEL PLD's (Win CUPL). I have now tried it on an
old version of this compiler and the error has gone! I haven’t had time
to program a device yet to try it, but things seem to be going in the
right direction!!
thanks |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in