## Overview of the AM2911ADMB The **AM2911ADMB** is a high-performance, 4-bit wide **Microprogram Sequencer** belonging to the Am2900 bipolar bit-slice family. It was originally manufactured by Advanced Micro Devices (AMD). The "DMB" suffix typically denotes a Hermetic Dual-In-Line Package (CerDIP) with Military-grade processing (MIL-STD-883). It is designed to control the sequence of execution of microinstructions stored in a microprogram memory. --- ### 1. Technical Specifications | Parameter | Specification | | :--- | :--- | | **Logic Family** | Bipolar (TTL Compatible) | | **Bit Width** | 4-bit (Cascadable) | | **Architecture** | Microprogram Sequencer | | **Package Type** | 20-pin CerDIP (Ceramic Dual-In-Line) | | **Operating Temp** | -55°C to +125°C (Military Grade) | | **Stack Depth** | 4-word Last-In, First-Out (LIFO) stack | | **Supply Voltage** | 5V Typical | --- ### 2. Functional Architecture The AM2911 is essentially a simplified version of the AM2909. While the AM2909 has a dedicated external input port for every source, the AM2911 shares inputs to reduce pin count. #### Key Internal Components: * **Microprogram Counter (µPC):** A 4-bit register that increments to point to the next sequential address. * **Address Multiplexer:** Selects the next address from one of four sources: 1. **External Direct Inputs (D):** For branching. 2. **Register (R):** For stored addresses. 3. **µPC Register:** For sequential execution. 4. **LIFO Stack:** For subroutines and returns. * **4x4 LIFO Stack:** Allows for nesting up to four levels of micro-subroutines. * **Internal Register (R):** A latch used to store a branch address or a data constant. --- ### 3. Pin Configuration Summary | Pin Group | Function | Description | | :--- | :--- | :--- | | **D0 - D3** | Direct Inputs | External address inputs for branching. | | **S0, S1** | Select Lines | Determines which source (Stack, µPC, Reg, or Direct) is sent to Y. | | **Y0 - Y3** | Address Outputs | The 4-bit address sent to the Microprogram ROM. | | **FE / PUP** | Stack Control | File Enable and Push/Pop control for the LIFO stack. | | **CP** | Clock Pulse | Synchronizes all internal register transfers. | | **RE** | Register Enable | Controls the loading of the internal 'R' register. | --- ### 4. Key Differences: AM2911 vs. AM2909 The AM2911 was designed to save board space (20 pins vs. 28 pins). * **AM2909:** Has separate "OR" inputs and "Ri" inputs for complex logic. * **AM2911:** Removes the "OR" inputs and shares the "D" inputs with the register logic to fit into a narrower 20-pin package. --- ### 5. Typical Application In a bit-slice computer architecture, multiple AM2911 units are "cascaded" to handle larger address spaces. For example, three AM2911s connected together create a 12-bit address sequencer capable of addressing 4096 words of microprogram memory.