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ICOM IC-720A Rotary Switch Replacement

2015-09-26 00:13  
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74HC00 Quad 2-Input NAND Gate High-Performance Silicon-Gate CMOS

A brief description: the counting pulse from J1-7 is “filtered” using 74HC00 NAND doors; it goes directly into the 4017, that start counting. The 4017 output goes to the 2222 transistor that drive the relay, and also goes to the diode matrix, to form the L1,L2,L4,L8 binary code needed for the 720′s microprocessor. The 4017 is powered directly to 7.5V, so there’s no need to convert this level to obtain the binary code so the microprocessors can use it directly (in fact, the 720 uP need about 7V logic levels. I don’t know why)

The 74HC00 is high-speed Si-gate CMOS devices that comply with JEDEC standard no. 7A. It is pin compatible with Low-power Schottky TTL (LSTTL). The 74HC00 provides a quad 2-input NAND function. The device inputs are compatible with Standard CMOS outputs; with pullup resistors, they are compatible with LSTTL outputs.

74HC00 Features

(1) Input levels: CMOS level

(2) ESD protection:

- HBM JESD22-A114F exceeds 2000 V

-MM JESD22-A115-A exceeds 200 V

(3)Multiple package options

(4)Specified from −40 °C to +85 °C and from −40 °C to +125 °C