Device for automatic modification of ROM contents by a system selected variable

• US 4,218,757 A
• Filed: 06/29/1978
• Issued: 08/19/1980
• Est. Priority Date: 06/29/1978
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Burroughs Incorporated (Terreno Realty Corp.)
• Inventors: Drogichen, Daniel P.
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Chan, E.
• Application Number:
  US05/920,557
• Time in Patent Office: 782 Days
• Field of Search: 364/900 MS File, 364/200 MS File, 365/94
• US Class Current: 711/102
• CPC Class Codes: G06F 9/24 Loading of the microprogram
• CPC Class Codes: G06F 9/26 Address formation of the next micro-instruction G06F9/28 takes precedence; Microprogram storage or retrieval arrangements

Abstract

A device for use with a digital computer for storing standard software used by the computer and modifying the address portions of the standard software prior to transmission to the computer. The device includes a ROM package containing a ROM within which is stored a standard software subprogram written assuming it is stored at an absolute location in the computer'"'"'s memory other than its actual location in the computer'"'"'s memory system. Also included in the ROM package is a base register which can be loaded, under control of the operating system software, with an offset value reflecting the difference between the actual starting memory system location of the subprogram stored in the ROM and the assumed absolute starting location of the subprogram. Each ROM word includes an extra bit to indicate whether the corresponding data word contains an address requiring relocation. As a word is read out of ROM, a gating circuit tests whether an address relocation is required. If the test is positive, the gating circuit gates the value in the base register into one input of an adder located on the ROM package, the other input to the adder coming from the data word read out of the ROM. The resulting modified data word outputted from the adder is sent to the computer. If the ROM output does not indicate that a relocation is required, the gating circuit provides a zero input to the adder so that the adder output reflects the unmodified input from the ROM.

Claims

1. An external memory device for processing data to be transmitted to a using device, comprising:

an addressable memory having an output and containing addressable storage locations;

a base register, said base register including a read/write storage memory and means for writing a pattern of data in said read/write storage memory;

gating means connected to the output of said base register and a first subset of the set of output bit positions of said addressable memory, said gating means responsive to selected data patterns from the first subset of said set of output bit positions of said addressable memory, said gating means for selectively gating the contents of said base register to the output of said gating means;

an adder having two inputs and an output, the inputs to said adder connected to a second subset of the set of output bit positions of said addressable memory and the output of said gating means respectively, the output of said adder for supplying processed data to said using device; and

output control means, responsive to the writing of data in said base register, said output control means for turning off the output of said adder.

2. The external memory device in accordance with claim 1 wherein said addressable memory is a read only memory.

3. The external memory device in accordance with claim 2 wherein said base register is further characterized as a static memory with a latched output.