AN ERROR LOGGING CIRCUIT OPERATABLE IN THE CASE OF SYSTEM FAULT

摘要

PURPOSE: An error logging circuit operated even when an error occurs in a system is provided to monitor a state of all systems and an error information using an I/O expander connected with a micro-controller and 12C bus which are capable of controlling a 12C bus and reading a memory and judge a changed stare information using a micro-controller and stores into a battery back SRAM. CONSTITUTION: A 87C652 micro controller(U1) controls a 12C bus and reads a memory. PCF8574 I/O expanders(U6, U7 and U8) generate an interrupt signal whenever the value of a port is changed and monitor a system state and an error information and is connected with a 12C bus for converting a parallel data into a serial data. An SRAM(U5) stores a system state and an error information read from the ports of the I/O expanders(U6, U7 and U8). A battery(B1) maintains a data of the SRAM(U5) in the power off state. ABT373(U3) and 74CBT3245(U4) are used as an address buffer. 74CBT3245(U2) is used as a data buffer. An AND gate(U9) receives a /RD and /WR signals of the 87C652 micro controller(U1) and generates a buffer control signal.