Parallel JTAG Interface
Published in issue 313, September 2002
This circuit is for an interface between the parallel port of a PC and a socalled JTAG interface. This type of circuit was originally developed by a company called Altera, which referred to it as the ‘Byteblaster’.The version described here is compatible with the Byteblaster (electrically it is almost identical). This has the advantage that programs written for use with the Byteblaster can also be used with this interface. The circuit itself is very simple. K1 is connected to the parallel port of the PC, whereas signals D0, D1 and D6 are brought to the JTAG connector via IC1. The output of the JTAG connector (TDO) is in turn fed back to the PC’s BUSY signal via IC1. Pin 7 of the JTAG connector is used to provide an extra output. This signal is brought to the SELECT input of the parallel port via IC1.
R1-R5,R9-R12,R15-R18 = 100Ohm
R6,R7,R8,R13,R14,R19,R20 = 10kOhm
C1 = 100nF
IC1 = 74HCT244
K1 = 25-way sub-D plug (male), PCB mount
K2 = 10-way boxheader
PCB, order code 020008-1
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Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.