Expansion of Indirect Addressing Registers Beyond the Architected Limit
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
The number of I/O devices which can be attached to an IBM System/38 computer system is limited by the number of base indirect address registers available and the number of these registers required for each device. This article describes increasing, beyond the architected limit, the number of registers available with only minor changes to microcode and an I/O channel controller. An extended range of registers is provided and indicated for use by a control word. The address indicating a position in the extended register can correspond to an address in the indirect address registers, but the control word indicates the use of the extended range of registers. Thus at a higher microcode level it appears that the same register is assigned to more than one I/O device.