GB1405322A - Data processing systems - Google Patents

Abstract

1405322 Microprogrammed data processing system SIEMENS AG 17 Jan 1973 [1 Feb 1972] 2402/73 Heading G4A A microprogram controlled processing system includes a first microprogram store containing a series of microinstructions and a mask, an address register for accessing the first store, and a second microprogram store accessed under control of a macrocommand to produce microinstruction parts which replace parts of a microinstruction read from the first store under control of the mask. Store 11 contains microinstructions common to all macroinstructions and store 13 contains parts of words to be used to modify a microinstruction from store 11 to convert the microinstruction to a microinstruction specific to a particular macroinstruction. Store 13 is addressed by the current macroinstruction and the data read out replaces part of the data read from store 11 selected under the control of a mask also read from store 11. In the embodiment of Fig. 3 a " read out macroinstruction " microinstruction is accessed from store 11 by an address table 17 via switch 18 path a. The next macroinstruction is thus loaded into register 15. Store 11 is sequenced via incrementer 21, switch 18 path e, or by jump addresses forming part of an instruction read from store 11 and fed to register 12 via switch 18 path d. The macroinstruction in register 15 addresses store 13 part of whose output via switch 18 paths b and c may select the first microinstruction in a sequence from store 11, e.g. an operand fetch sequence. Parts of the instructions read from store 11 are replaced by the output of store 13 under the control of the mask M read from store 11. A gate assembly is described for switch 18 with a feedback from output to input to enable the switch to function as a latch. The stores 11 and 13 may be read only program stores, store 13 containing modifying parts for the output of store 11, and the addresses in store 11 of various microinstruction sequences, e.g. read out macroinstruction, operand fetch etc. sequences.