Buffered Jtag or Not Buffered

[BirdieMod]

It prevents ground loop errors between the receiver and home computers since they are both running on ac power. Best to go buffered on home pc. Laptops do not need the buffer since the are allready isolated from the ac line.

[BirdieMod]

Probably, Guess I always keep mine charged so never tried it that way.

[DSSNobody]

It prevents ground loop errors between the receiver and home computers since they are both running on ac power. Best to go buffered on home pc. Laptops do not need the buffer since the are allready isolated from the ac line.

The IRD is running on AC power.

However, the laptop or computer are running on DC power. The power supply in the computer converts the 120v AC into 12v DC and lower to run the internal devices of the computer/laptop.

The highest voltage coming out of a standard computer/laptop (after you pass through the power supply) should be 12v DC.

My understanding was the buffered JTAG allowed you to control the voltage being sent to the IRD. Standard output on a LPT port is 5v DC. Some IRDs can take 5v DC on the chip, others (301 - I believe) are set for 3.3v DC. Hence running 5v DC to a 3.3v DC could burn out the chip.

The buffered JTAG allows you to change your voltage.

Please correct me if I am wrong, but I think this is the case.

[skinerd]

The IRD is running on AC power.

However, the laptop or computer are running on DC power. The power supply in the computer converts the 120v AC into 12v DC and lower to run the internal devices of the computer/laptop.

The highest voltage coming out of a standard computer/laptop (after you pass through the power supply) should be 12v DC.

My understanding was the buffered JTAG allowed you to control the voltage being sent to the IRD. Standard output on a LPT port is 5v DC. Some IRDs can take 5v DC on the chip, others (301 - I believe) are set for 3.3v DC. Hence running 5v DC to a 3.3v DC could burn out the chip.

The buffered JTAG allows you to change your voltage.

Please correct me if I am wrong, but I think this is the case.


If you want to get technical, the IRD also runs on DC, the incomming AC is rectified to DC then fed to a chopper to get pulsated DC to run a transformer that supplies other components with power, which is further rectified to output 3.3 and other voltages. The low voltage power to the board is completelty isoloted from the AC line. If the IRD is the type with only a 2 conductor cord, the there is no ground loop possible, if it has a 3 wire cord, then the receiver case is grounded to the electrical system ground of the building. Ground looping is the least of the concerns jtagging. A buffered jtag has a 74hc244 chip between the parallel port and the jtag port to buffer the signals going back and forth between the 2 devices so there is no direct connection, except for the ground so that both deveces will be at the same ground potiental. I have used both buffered and unbuffered, both will work fine, the buffered type adds a little more security since there is no direct connection between the parallel port and the jtag port.

[DSSNobody]

Skinerd,

What is the point of using a buffered JTAG (if it is not to isolate the IRD from the potential burnout caused by a higher voltage from the LPT port)?

I have made several simple jtags. I am currently working on a buffered jtag (with no success, but I keep learning from my mistakes).

Do I actually need a buffered jtag to protect my 301 from burnout?

[skinerd]

Skinerd,

What is the point of using a buffered JTAG (if it is not to isolate the IRD from the potential burnout caused by a higher voltage from the LPT port)?

I have made several simple jtags. I am currently working on a buffered jtag (with no success, but I keep learning from my mistakes).

Do I actually need a buffered jtag to protect my 301 from burnout?

You don't nescessarily NEED a buffered jtagf if the unbuffered tpye works for you, it's just more secure and safer, but used cautiously, the unbuffered usually works fine.

[t160hq]

While the buffered jtag does provide limited protection bewteen the comp and the receiver that is not it's main function.

Communication bewteen different devices, in some cases, requires converting the way the data is transmitted. This conversion can take several forms. Speed of transmission. Signal levels may need to be increased or decreased depending on the device you are communicating with. Voltage levels may need to be modified (eg 3.3v vs 5.0v tsop).

As in all electronic communication noise is also a factor. Hence the need for short wire runs on non-buffered jtag's. The buffered jtag reduces this wire length problem by filtering out extranous noise created in the wire bewteen the comp and the receiver.

We are dealing with a printer port used to communicate with a receiver. The port was designed to work with a printer. Not a receiver. The receiver does not follow the same communication standards as the printer. Although they are very close which is the reason it all works.

The buffered unit is also a bi-directional device. Which means it serves the same function both ways.

So with a buffered jtag both the receiver and the comp get the correct transmission of data to perform the function. In both read and write modes. This means better reliability of reads and writes bewteen the devices.

In data communication close is not good enough. It has to be exact or errors will occur.

t160hq