4D systems Picaso MD1, Руководство пользователя, Страница: 45 / 47

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µ V G A -PICASO- MD1
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13 Power-Up Reset
When the µ V G A -PICASO- MD1 comes out of a power up reset it initialises the Video
Graphics RAM and the internal Display registers. Allow up to 500ms before attempting to
communicate with the module
. The power up sequence of events should be as follows:
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Allow 500ms after power-up for module to settle. Do not attempt to communicate
with the module during this period. The µ V G A -PICASO- MD1 may send garbage on
its Tx Data line during this period, the host should disable its Rx Data reception.
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Within 100ms of powering up, the host should make sure it has its Tx line pulled
HIGH. If the host Tx ( µ V G A -PICASO- MD1 Rx) is LOW or floating after the 100ms
period, the module may misinterpret this as the START bit and lock onto some
undesired Baud Rate. If the host has a slow wake up time, i.e. less than 100ms, its
Tx line maybe floating. This can be easily resolved by adding a pull up resistor on
the host Tx line which will ensure the module does not encounter a false START bit.
The pull up resistor can be any value within 10K to 100K.
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The host must transmit the ASCII ‘U’ (capital U , 55 hex) as the first command so the
module can lock onto the host’s serial baud rate. This is called “ Auto Bauding ”. The
module will respond with an ‘ ACK ’ (06h). See section 7.
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The module is now ready to accept screen function commands from the host.