What's the maximum length I can run 4 JTAG signals on a 2-layer non-controlled board?

[jdhar]

What's the maximum length I can run the 4 JTAG signals on a 2-layer non-controlled impedance board (approx)? I want to put two FPGA's on my board, but the problem is with one being a 244-pin FQFP, the other one will be some distance off, so Im' not sure if I can chain them together.

Jai

 

[pvskt]

jtag length

There is no specific length standard for routing the JTAG signals. Since its not an impedance controlled board, the PCb critical length property comes into picture.....AI guess you are using FR4....For FR4 the critical length would be 3 inches for the JTAG signal.

 

[jdhar]

jtag layout guidelines

What kind of rise-time did you make this estimate on? .5ns?

 

[pvskt]

routing jtag signals

1ns