Microprogrammed control unit for executing a string transfer instruction at increased speed.

摘要

For transferring bytes forming a character string or a bit string at a high speed in response to a string instruction, a microprogrammed control unit comprises a storage facility (13) storing a micro-instruction code set, a program counter (14) memorizing an address code indicative of the address assigned to the micro-instruction code accessed, a decoder (17) supplied with the micro-instruction code and producing various control and/or data signals, a loop counter (19) storing a data code indicative of the number of bytes not to be transferred and associated with a subtracter (20), a count value detector (21) checking the data code to see whether or not the value indicated by all of the bits and the value indicated by higher order bits respectively reach predetermined values and a branch controller (18) responsive to the control signals and executing first and second branch operations in the presence of reporting signals indicative of reaching the predetermined values, respectively, and plural bytes are transferred in a single transferring operation after the first branch operation, but a single byte is transferred in the single trans ferring operation for completing the string instruction between the first and second branch operations.