JTAG pin TDO current consumption and JTAG problems

Go To Last Post
5 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,

I am using ATMEGA32L.

The atmel datasheet mentions that TDO pin should have pullup, if not used in the circuit, when JTAGEN fuse is enabled. If left floating, draws considerable static current.
The numbers are not mentioned anywhere. Any idea about this number???

Another thing, I get tremendous noise on RXD pin whenever I connect JTAG ICE on target board. As I am using UART, the repective interrupts are enabled and even if external device is not communicating, execution is interrupted continuously. If I remove JTAGICE from target board, everything works fine. I have checked board thoroughly, but unable to find any relation between RXD and JTAG pins.

Any comments???

Sanjiv.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Sanjivb wrote:
The atmel datasheet mentions that TDO pin should have pullup, if not used in the circuit, when JTAGEN fuse is enabled.

Where does it say this? I just looked at the datasheet and couldn't find this.

Dave

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

dharper wrote:
Where does it say this?

At the bottom of page 33 of the ATmega32(L) data sheet (doc2503.pdf), it states:
Quote:
The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP
controller is not shifting data. If the hardware connected to the TDO pin does not pull up
the logic level, power consumption will increase.

Don

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

donblake wrote:
At the bottom of page 33 of the ATmega32(L) data sheet (doc2503.pdf),

Sure enough - helps to have the latest datasheet. I'm a little surprised at this comment, though - this appears to be an Atmel specific issue. I just checked the IEEE 1149.1-1990 (JTAG) spec and it mentions nothing about this for TDO. Unused inputs obviously need to be pulled up and this is done automatically on TDI, TMS and TCK when the JTAGEN fuse is programmed. I wonder if things are set up such that the TDO pin acts as an input when it is not specifically in a shift state?

Dave

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Also refer Pg. 58 and Pg.226 for TDO issue.
Only thing not mentioned is numbers. Any idea abt. this??

Also, anybody faced RXD noise problem??

Sanjiv.