EJTAG
From t-hack.com - Hack X300T / X301T
Contents |
JTAG on the SMP863x
eJTAG is a debug interface specified bei MIPS. it is an extension of the standard JTAG specification.
Since the SMP863x CPU has a MIPS core, it also has a JTAG port :) But it is deactivated by default :(
In case of the X300T there is a eJTAG connector and also a jumper to activate the eJTAG, as shown in the image below. The jumper can be permanently shorted. For DIT9719 PCB follow DIT9719 PCB.
Only the pins TDI, TDO, TMS, TCK and GND are needed to make the interface work.
eJTAG Pinout of the X300T
How to get an Interface
The easiest solution to use the eJTAG interface is to build an unbuffered DLC5 JTAG interface found below.
If you decide to buy a JTAG interface you should be aware the the 14pin header of most JTAG interfaces use a different pinout then the eJTAG. So you might have to fix the cable to correct the pinout.
DLC5 JTAG
or
- Advantage
- easy to build
- very cheap
- no power supply needed
- Disadvantage
- interface cable has to be rather short to avoid transmission errors. 10-20cm is probably the maximum length. shorter == better
Wiggler Clone JTAG
An alternative is to use a Wiggler-Clone .. (the original Wiggler interface cost 150$)
- Advantage
- interface cable can be a bit longer .. probably 30-50cm, but also in this case, shorter == better
- Macraigor software can be used
- the target systems CPU is protected by the buffer
- Disadvantage
- more complicated to build
- more expensive but still cheap
