My second prototype is a PCB with about 7 x 6 cm size with the followingcomponents on board:
FT2232C with 93C56 EEPROM
Step up/down regulator to guarantee 5.0 Volt from 4.5 to 5.5 USB Voltage.
RS-232 Level Shifter (MAX3241)
ADuM1401BRW I-Coupler for JTAG port level shifting and electrical isolation.
RS-232 connector D-SUB9
JTAG Connector
Be aware, the design has some flaws:
The I-Coupler does not work at highest speed (ca. 6 MHz). It can only be used with 3 MHz and slower. The reason is, that the couplers have a rather large propagation delay of about 50 nsec.
The I-Coupler can only be used for 3.3V and 5V targets. Future target voltages, especially 2.5 and 1.8V are not supported.
The reset signals SRST and TRST are not 3-state signals. Depending on the schematics of the target this can cause problems.
schematic.pdf
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