integrated technology express, inc. ittm-an-99007, july. 1 page 1 of 1 application note of it8761f for power on strapping circuit july 1, 1999 ? power on strapping circuit needs extra attention when a ? 0 ? setting is selected description: due to it8761 rev. b power on strapping pins selection, a ? 0 ? 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 ? 0 ? 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. 4.7k 7407 1 2 it8761 1488/89 txd1/rts1#
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