TIET890AGA

The TIET890AGA is Texas Instruments' TIET890A microsequencer in the GA pin-grid-array package, a microprogram address generator for bit-slice and other microcode-based processors. Built with IMPACT-X technology, it runs ECL internal circuitry behind TTL-compatible inputs and outputs, and it is functionally equivalent to the SN74AS890 while targeting higher performance. It selects a 14-bit microaddress from one of eight sources to drive up to 16,384 words of control store from a single chip, addressing those locations either sequentially or through conditional branches, all from a 5-volt supply. A nine-word-deep stack and multiway branching let the microcode handle nested routines and complex decision trees without external address logic.

Key Features

• 14-bit addressing - generates microaddresses for up to 16,384 words of microcode from one device, sequentially or by conditional branch.
• Eight address sources - selects the next microaddress from any of eight sources for flexible microprogram flow.
• Nine-word LIFO stack - a nine-deep last-in first-out stack supports nested subroutines and multiway branching.
• Two loop counters - two independent loop counters handle iterative microcode without extra logic.
• Real-time interrupts - interrupt support lets the sequencer respond to events during microprogram execution.
• IMPACT-X performance - ECL internal circuitry with TTL I/O delivers speed beyond the Advanced Schottky SN74AS890 it is functionally equivalent to, from a single 5V rail.
• Diagnostic read pointer - an independent read pointer aids microcode diagnostics and debug.

Typical Applications

• Bit-slice processor control - sequencing microcode for custom CPUs built from bit-slice ALUs.
• High-speed microcoded engines - signal-processing and controller designs needing fast next-address logic.
• Legacy system support - sustaining microcoded systems that specified the TIET890A.
• Custom instruction decoders - driving wide control stores in instrumentation and defense-grade controllers.

Unique Advantages

• Faster AS890 equivalent - functional equivalence to the SN74AS890 plus IMPACT-X speed lets it serve as a higher-performance drop-in for that architecture.
• 64-instruction set - a rich instruction repertoire covers complex branching, looping, and subroutine control in microcode.
• Debug-friendly - the independent read pointer gives visibility into the microprogram stream for diagnostics.

Why Choose TIET890AGA?

The TIET890AGA is the microsequencer to specify when a microcoded or bit-slice design needs the SN74AS890 feature set with IMPACT-X speed and TTL-compatible interfacing. Its 14-bit addressing, eight-source selection, nine-word stack, dual loop counters, and 64 instructions give designers full control over microprogram flow, and its diagnostic read pointer eases bring-up. It remains an important part for building and maintaining high-performance microcoded systems. Because it is functionally equivalent to the SN74AS890, existing microcode and board designs around that sequencer can move to the TIET890A for added speed with minimal rework.

Contact us for pricing, availability, and lead time on the TIET890AGA, and tell us your control-store depth and system so we can confirm the fit.