Hello parport list
I am trying to protect my parallel port from damage from a custom
built device. A sensor, labeled Sensor in the diagram, is normally
in a state where current is sinked through connection 2. This pulls
the line to the buffer down. When the sensor responds to an event
connection 2 becomes high impedance and the line-to-buffer goes high.
This is all OK.
I am trying to protect the parallel port from the following two situations:
(1) a high value is written to the parrallel port pin while the
line-to-buffer is low. This may happen while booting the machine
with the device connected. I inserted the buffer to protect the
port from sourcing too much current.
(2) a high occurs on the line-to-buffer while a low is asserted on
the port. A situation that might sink to much current. I am
assuming the high input impedance of the port protects it
in this situation.
Am I correct? Is this a reasonable way to do this?
Thank you,
Daniel
Gnd |
|-------------------------|------------| port ground pin
_________ | | |
| | | ____|___ |
| 1 |-----| | | |
| Sensor | |74HCT244| | data pin: SIIG
| 2 |-----------|--------------| buffer |--------| parallel pro
| | | |________| | port (BPP mode)
| 3 |-----| \ | |
| | | / 4.7 KOhm |
|_________| | \ 5V
|_____|
|
|
5V
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This archive was generated by hypermail 2b29 : Mon Aug 20 2001 - 20:39:18 EDT