Programming arrangement for programmable devices

Abstract

A programmable matrix has improved programming circuitry which allows the matrix to be programmed without raising the output terminals or power supply to higher than normal voltage levels. The circuitry includes a bidirectional output buffer and a multi-purpose input pin. The output buffer is provided with a control input and at least one buffer output. A switching device in the buffer provides a path to ground for programming current when a programming enable signal is applied to the control input and a concurrent operating level voltage pulse is applied to a selected buffer output. Programming current may be supplied via a dedicated input pin, but is preferably supplied via the multi-purpose input pin. A higher than normal operating voltage signal applied to the multi-purpose input pin acts to produce the programming enable signal which is subsequently applied to the buffer control input. This arrangement makes it unnecessary to elevate the voltage on the power supply input or the buffer outputs for programming purposes. The buffer outputs are isolated from programming currents and voltages by a second switching device in the bidirectional output buffer. The programming arrangement may be used with PROMs, PLAs and other programmable matrices.

Dependencies are inferred from the claim text.