56800/E JTAG adaptor

Posted by Petr Hapal on 18 January 2013 | 4 Comments

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I've described tools needed for development in my last post. JTAG adaptor is one of them. There are two low cost possibilities - CodeWarrior USB TAP and LPT JTAG. The biggest "pro" for USB TAP is that USB ports are everywhere. However flashing time and debugging speed is the same as in case of LPT JTAG. In this post you will find a construction of LPT JTAG. The biggest "con" is need of hardware LPT port - this is a problem of new laptops. If you would like to buy or build USB -> LPT converter - do not try this, it doesn't work (I've tried cheap USB-LPT from ebay and USB-LPT based on AVR MCU, both not working). Only chance is probably PCI or PCMCIA card.


CodeWarrior USB TAP JTAG adaptor

You can see LPT JTAG schematic on picture below. There is nothing to say about it. It is based on 74HC244 buffer (do not use HCT), 74LS00 and some passives. LED D1 indicates power supply from target application, button S1 is RESET. K2 connector is a Freescale standard JTAG connection which can be found on all Freescale kits.


LPT JTAG adaptor schematic

Whole device is designed for single sided PCB with few wire connections. Wiring is thick enough to be able to etch it at home. JTAG and target device is connected using flat wire. If a flat wire is long (more than 10cm) I recomend use of ferite core for better EMI imunity.

LPT JTAG adaptor PCB


Qty Value       Device      Parts          
1   2N2222A     2N2222      T1        
1   3MM GREEN   LED3MM      D1                        
3   5k1         R-EU_0207/7 R6, R7, R8
3   47k         R-EU_0207/7 R1, R2, R9    
2   51R         R-EU_0207/7 R5, R3         
1   74HC244N    74HC244N    IC1     
1   74ALS00N    74ALS00N    IC2       
1   470R        R-EU_0207/7 R4
1   CAN 25 V 90 M25HP       K1             
1   MLW14A      ML14L       K2             
1   P-B1720     10-XX       S1   


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