MIL-DTL-62739A

Abstract

This specification covers a Clock/Display Driver Printed Wiring Assembly referred to herein as the PWA. This is one of six printed wiring assemblies which comprise the Simplified Test Equipment/Internal Combustion Engine-Reprogrammable (STE/ICE-R) Vehicle Test Meter (VTM) (see Drawing 12259265). <b><u>Intended Use:</u></b> The PWA contains a 16-bit resetable real time clock with latch and timing circuitry. High and low bytes of the latched clock data can be placed on BUS 0 - BUS 7 (board pins 21-28) independently. (Board pins will hereafter be referred to as P1-XX where XX = the pin number.) The clock count is incremented at one fourth the frequency of the signal at P1-45. The clock section also provides a Q pulse output (P1-42), a self-test output (P1-40), and an EF4 output (P1-39). The Display Driver consists of four latches (U3, U4, U5, U6) which can each latch 8 bits of data off BUS 0 - BUS 7. Each output of each latch drives the base input of an open collector darlington transistor pair. When a logic level 1 is present at the base input, the collector input of the darlington pair will sink current, lighting up a segment of an external display which is pulled up to +5 Vdc. Connected to each of the collector inputs is a 510 ohm resistor to ground which keeps the external display segment partially on when it is not being driven by the darlington pair. The PWA also provides an output from U22, pin 11 to P1-41. The PWA is military unique because it is designed specifically to be a component of the Simplified Test Equipment/Internal Combustion Engine - Reprogrammable (STE/ICE-R) Vehicle Test Meter (VTM), and to withstand environmental conditions which exceed commercial requirements. <br>