LM9830VJDX NSC [National Semiconductor], LM9830VJDX Datasheet - Page 44

• Manufacturer Part Number: LM9830VJDX
• Description: LM9830 36-Bit Color Document Scanner
• Manufacturer: NSC [National Semiconductor]

Printer Passthrough Block Diagram
Notes:
V
may be rectified as well to provide additional current.
If the LM9830’s TRISTATE output is not forced to ground when the LM9830 power is off, then it needs a pulldown resistor to
ground.
The 74HCT373 needs to pass 4 lines from the PC to the printer, the 74HCT244 controls 5 lines from the printer to the PC. The
latch is needed to hold the 4 inputs to the printer in the state they were in before the LM9830 left the transparent mode. It is possi-
ble that a simple tristate buffer (74HCT244) could be used instead of the latch, with pullups/pulldowns defining the signals sent to
the printer when the LM9830 is active. It is also possible that one signal (probably INIT) could always be simultaneously connected
to the printer port and the LM9830, allowing just one 74HCT244 to implement the printer passthrough function.
The final recommended schematic for this mode is an applications issue and will be determined after testing with final silicon.
The design requirements are:
TRISTATE
LATCH
D0-D7
STROBE, AUTOFEED,
SELECT IN, INIT
ACK, BUSY, PE,
SELECT, ERROR
PASSTHROUGH
Computer
To
is generated by rectifying the control outputs from the PC and printer parallel ports. If needed, the 8 bit data lines
Control Signals
5
Scanner Active
LM9830 sends/receives
Inputs to LM9830
LM9830 Outputs
+5V
0V
4
+5V from Scanner Power Supply
8
5
4
Databus
LM9830
PassThrough
0V
5V
Tristate
Tristate
Tristate
74HCT244
TRISTATE
V
PASSTHROUGH
74HCT373
LM9830 Power Off
0V (through pulldown, if necessary)
5V (through pullup) (latches previous states)
Tristate
Tristate
Tristate
LATCH
BIAS
5
4
Printer
To