## AM2964BPC: Dynamic Memory Controller The **AM2964BPC** is a high-performance Dynamic RAM (DRAM) controller and address multiplexer, originally manufactured by Advanced Micro Devices (AMD) in the 1980s. It was designed to simplify the complex interface between a CPU and DRAM, specifically for the 16K, 64K, and 256K memory generations. --- ### 1. Key Technical Specifications | Parameter | Description | | :--- | :--- | | **Logic Family** | Bipolar (TTL) | | **Package Type** | PDIP-40 (Plastic Dual In-line Package) | | **Functions** | Address Multiplexing, Refresh Counter, RAS/CAS Control | | **Memory Support** | 16K, 64K, and 256K DRAMs | | **Operating Voltage** | +5V (Standard TTL) | | **Speed** | High-speed (Schottky technology) | --- ### 2. Core Functional Blocks The internal architecture of the AM2964BPC is divided into several critical sections that automate the DRAM management process: * **Address Multiplexer:** It takes an 18-bit input address (from the CPU) and splits it into two 9-bit halves (Row Address and Column Address) to be sent to the DRAM sequentially. * **Internal Refresh Counter:** To prevent data loss in DRAM, the chip contains an 8-bit counter that automatically tracks which memory rows need to be refreshed. * **RAS/CAS Control Logic:** It manages the timing for **Row Address Strobe (RAS)** and **Column Address Strobe (CAS)** signals, ensuring the DRAM captures the address at the correct moment. * **Burst/Cycle Modes:** Supports various refresh modes to ensure memory stability without heavily interrupting the CPU's processing time. --- ### 3. Pin Configuration Overview The AM2964BPC is a 40-pin device. Below are the primary signal categories: | Pin Category | Name | Function | | :--- | :--- | :--- | | **Inputs** | $A_0 - A_{17}$ | 18-bit Address input from the processor. | | **Outputs** | $Y_0 - Y_8$ | Multiplexed 9-bit address output to the DRAM chips. | | **Selection** | $S_0, S_1$ | Selects between Row address, Column address, or Refresh address. | | **Refresh** | $REFRQ$ | Refresh Request input signal. | | **Power** | $V_{CC}, GND$ | 5V Power Supply and Ground. | --- ### 4. Why was it used? Before dedicated memory controllers like the AM2964BPC, designers had to use dozens of individual TTL logic gates to manage DRAM timing and refreshing. The AM2964BPC offered several advantages: 1. **Space Savings:** Replaced approximately 10-15 standard logic chips. 2. **Timing Precision:** Guaranteed internal propagation delays, reducing "glitches" in memory access. 3. **Ease of Design:** Handled the cumbersome 128 or 256-cycle refresh requirements of early RAM automatically. ---