10-26-2009 06:51 AM
We are using EXTEST Instruction to drive IO pins of the CPLD and it is working fine.However we came across one scenario and please give your inputs on following case. We have driven two XCR3128XL CPLD pins to HIGH (Logical 1) and another two IO pins to LOW (Logical 0) using EXTEST Instructions.
Now we need to make another one IO pin to HIGH without altering the state of the other pins.
Is there any specific instruction or approach to achieve this?
Please help on this as we struggling in this for lot of time. (We can use SAMPLE Instruction first and sample all pins and keep the state of others pins to existing pin states and we can drive that specific IO to HIGH. However we feel that it is required lot of processing and we are looking for any other efficient solutions)
10-26-2009 12:14 PM
Not sure if I understood you question correctly.
There is a good software -- TopJTAG Probe http://www.topjtag.com -- for probing and interactively controlling pin states via JTAG/boundary-scan. Just with mouse clicks you can choose what pins to drive high or low in EXTEST mode.
10-26-2009 09:12 PM
Thats good... but we are trying to implement the same thing with one JTAG Controller in our design. So with mouse click, we can choose the specific pin and drive it to LOW or HIGH using EXTEST instruction.
I would like to understand these in low level i.e.
is the data is shifted through all the boundary scan cells (not altering existing boundary cell values and driving only the specific cell (pin) value) to drive that pin to HIGH ?
is there any other instruction which does not shift values to all boundary cells and make only that pin to HIGH?
Also we are having XCR3128XL CPLD and we would like to know how to program it using In System Programming (ISP) instructions.