Description: Due to IT8761 Rev. B power on strapping pins selection, a 鈥?鈥?/div>
setting may not be strapped in correctly.
Cause:
IT8761 chooses TXD1 and RTS1# pins for power on strapping
setting, since these two pin also connect to 1488/1489 type line
driver and some of the line driver internally have +12V pull up
with a 11K ohm resistor, this will cause the 鈥?鈥?setting not
correctly strapped.
Suggestion: (1) Choose a small enough value pull down resistor to make the
strapping line voltage below 0.5V when system is reset. A
suggested resistor value is 680 ohm.
(2) Implement a redundant gate between IT8671 and line driver
to isolate the interfere of the internal pull up of 1488/89 line
driver as following circuit.
IT8761
TXD1/RTS1#
1
7407
2
1488/89
4.7K
ITTM-AN-99007, July. 1
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