Method for Patching Errors in Prom-Based Microsequencer Code
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
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.