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Method for Patching Errors in Prom-Based Microsequencer Code

IP.com Disclosure Number: IPCOM000062449D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Martin, ES: AUTHOR

Abstract

A method is described for reducing the development cost of PROM-based programs by enabling the writing and execution of modified routines in the unused portions of the original PROMs. The method described consists of (a) writing a conditional jump instruction with a blank target address at the beginning of a routine, (b) putting the address of the modified routine into the target address when required, and (c) enabling the jump by causing the conditions of the conditional jump instruction to be satisfied. Normally, microsequencers are controlled by programs contained in ROMs (read-only memories) or PROMs (programmable read-only memories). During development, PROMs are normally used, and if errors are found during debug, a new PROM must be burned to correct the error.

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Method for Patching Errors in Prom-Based Microsequencer Code

A method is described for reducing the development cost of PROM-based programs by enabling the writing and execution of modified routines in the unused portions of the original PROMs. The method described consists of (a) writing a conditional jump instruction with a blank target address at the beginning of a routine, (b) putting the address of the modified routine into the target address when required, and (c) enabling the jump by causing the conditions of the conditional jump instruction to be satisfied. Normally, microsequencers are controlled by programs contained in ROMs (read-only memories) or PROMs (programmable read-only memories). During development, PROMs are normally used, and if errors are found during debug, a new PROM must be burned to correct the error. As most microsequencers have multiple PROMs, this can be an expensive proposition. If new types of PROMs are being used, they can also be in short supply. This method configures the hardware so that upon finding errors, unprogrammed bits in the PROM can be programmed to allow corrections to be placed in unused portions of the PROM. The figure shows a basic microsequencer design. Depending on the type of microsequencer 10 used either a + or - input to the test input 11 will cause the program to jump during a conditional jump instruction. Also, the unprogrammed output of PROMs 12 can vary, some are and some are -. For the particular set of PR...