Integrated Technology Express, Inc. Application Note of IT8761F for Power On Strapping Circuit July 1, 1999 Ø 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. IT8761 TXD1/RTS1# 1 7407 2 1488/89 4.7K ITTM-AN-99007, July. 1 Page 1 of 1