Revision 1.1
8
A 74HC374 octal D flip-flop is used to buffer the digital outputs. Output data from the target
microcontroller is latched by the DOUT port pin which is generated by U13 the 74HC138 3-8
line decoder. The truth table for the 74HC138 is shown here.
MUXA
MUXB
MUXG2A 74HC138 Active Low Output
0
0
1-0
Y0 – USB Read
1
0
1-0
Y1 – USB Write
0
1
1-0
Y2 – DOUT
1
1
1-0
Y3 – DIN
1-0 - Indicates a high to low transition
POWER SUPPLY
The DLP-IO16 takes all needed operational power from the host PC's USB port. When the host
PC goes to Standby mode, the DLP-IO16 will also go to Standby mode after 3 milliseconds of no
USB bus activity. If the 5-volt power for the DLP-IO16 board is supplied by the target
electronics via the Digital I/O Interface connector (JP3) then the jumper at JP4 must be removed.
To help ensure compliance with the USB specification, power for the USB interface electronics
(FT8U245AM) should be supplied by the host PC’s USB interface.
