Browse Prior Art Database

Use of Cyclic Redundancy Code for Testing ROM And RAM in a Writeable Control Store

IP.com Disclosure Number: IPCOM000102246D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Dobkin, RJ: AUTHOR

Abstract

This article describes the use of cyclic redundancy code (CRC) checking to determine the validity of stored data and the indication by means of light-emitting diodes (LEDs) to show which of two components is faulty.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 58% of the total text.

Use of Cyclic Redundancy Code for Testing ROM And RAM in a Writeable Control Store

       This article describes the use of cyclic redundancy code
(CRC) checking to determine the validity of stored data and the
indication by means of light-emitting diodes (LEDs) to show which of
two components is faulty.

      Some existing processors store their control microcode in read-
only storage (ROS).  A writeable control store system has been
implemented which consists of an erasable programmable ROM (EPROM)
and fast static RAM (SRAM).  The EPROM contains microcode to be
loaded to the SRAM for possible later modification.

      The drawing is a functional block diagram of the technique
disclosed herein.  On power-up, the processor reads just enough data
from the 64Kx8 EPROM to fill the 8Kx36 SRAM.  A MUX determines
whether the input to a microcode transfer latch (MTL) comes from
EPROM or SRAM.  In this phase the MUX selects input from the EPROM.
Each 36-bit microcode word is stored in five consecutive bytes of the
EPROM.  As each byte is read, it is placed in its proper position in
the MTL.  The last four bits of the fifth byte are discarded.  Then
the 36-bit word is shifted through a CRC register and written to the
SRAM.  Then the next five bytes are read from the EPROM, and the
cycle continues until the SRAM is fully loaded.

      The last microcode word contains the CRC check, which, when run
through the CRC register, will zero out the CRC register,...