Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Desautels, JC: AUTHOR [+3]
The storage capacity of a controller is increased by an add on device that fits between the controller and storage. Its purpose is to provide additional storage addressability and to repower the storage's address, data, and control lines (Fig. 1).
The storage capacity of a controller is increased by an add on device that fits
between the controller and storage. Its purpose is to provide additional storage
addressability and to repower the storage's address, data, and control lines (Fig.
The add on device is a synchronous interface; that is, data is expected back at the controller quickly, so it can be clocked into a register. The add on device's repowering and gating circuits for storage select cause an additional delay. Without the presently described technique, data returning from storage on a read operation is too late to meet the clock pulse, creating incorrect data in the register.
The preselect technique generates the memory select with the same clock that generates the controller select without waiting for the controller's select circuit delay, and then adding to that delay the circuit delay of the add on device's gate and power logic. Therefore, the storage unit sees the select at the same time whether it was generated by the add on device's logic or by the controller without the add on device. Thus, the data from storage returns to the controller at the proper time to be clocked into the controller's registers (Fig. 2). The select coming from the controller is then logically ORed with the select generated by the add on devices, which provides the proper select pulse width to the storage unit.
This technique permits additional storage to be added to the system without degradin...