Question

Sketch a diagram showing interfacing of two chips of RAM having a size of 2k × 8 to the 8051 microcontroller. Write its memory map.

Answer 1

To interface two 2K × 8 RAM chips with the 8051 microcontroller, we will design a basic circuit diagram and also provide a memory map. The 8051 microcontroller has a limited amount of internal RAM and provides the necessary connections to interface external RAM.

### Overview of the 8051 Microcontroller

- **Microcontroller:** 8051
- **Internal RAM:** 128 bytes
- **Address Bus:** 16-bit (can address 64KB of external memory)
- **Data Bus:** 8-bit

### RAM Chip Details

- **Chip Size:** 2K × 8 (2048 × 8 bits)
- **Total Size of Two Chips:** 2K + 2K = 4K (4096 bytes)

### Chip Interfacing Diagram

Below is a description of how to sketch the interfacing of the two RAM chips to the 8051 microcontroller.

#### Diagram Components

1. **8051 Microcontroller**
   - Connect the **Address Bus (A0-A15)** from the microcontroller to the address inputs of the RAM chips.
   - Connect the **Data Bus (D0-D7)** from the microcontroller to the data inputs and outputs of the RAM chips.

2. **RAM Chips**
   - Each RAM chip will have an **Enable (E)** pin which will determine whether the chip is active or not.
   - The two RAM chips will have **Chip Select (CS)** pins to enable/disable the chips.

3. **Decoding Logic**
   - Use a simple address decoder (e.g., a combination of AND gates) to generate the Chip Select signals for the RAM chips based on the higher address lines of the microcontroller.

### Circuit Diagram

Here’s a basic sketch description of the interfacing:

```
            +-------------+
            |   8051      |
            |  Microcontroller  |
            +-------------+
                |     |
                |     |
                |     |
               A0-A15   D0-D7
                |     |
                |     |
          +----------+----------+
          |                     |
       +-----+              +-----+
       | RAM1 |            | RAM2 |
       | 2K×8 |            | 2K×8 |
       +-----+              +-----+
          |                     |
          |                     |
         +E                     +E
         |                     |
        CS1                  CS2
          |                     |
   +------+--------+   +------+--------+
   | Address Decoder|   | Address Decoder|
   +----------------+   +----------------+
```

### Memory Map

The memory map for the interfacing of two 2K × 8 RAM chips with the 8051 microcontroller is as follows:

- **Internal RAM of 8051:**
  - **Address Range:** 0x00 to 0x7F (128 bytes)

- **External RAM (RAM1):**
  - **Address Range:** 0x80 to 0xFF (2K Bytes)
  
- **External RAM (RAM2):**
  - **Address Range:** 0x100 to 0x17F (2K Bytes)

### Detailed Memory Map

| Address Range | Description                  | Size      |
|---------------|------------------------------|-----------|
| 0x00 - 0x7F   | Internal RAM of 8051        | 128 Bytes |
| 0x80 - 0xFF   | External RAM1 (2K × 8)      | 2K Bytes  |
| 0x100 - 0x17F | External RAM2 (2K × 8)      | 2K Bytes  |

### Address Decoding Logic

To select RAM1 and RAM2 using the address lines, we can implement the following logic:

- **For RAM1 (Address Range 0x80 - 0xFF):**
  - Connect the most significant address line (A7) to the Chip Select (CS1) of RAM1.
  - **Logic:** CS1 is active when A7 = 1 (indicating addresses 0x80 - 0xFF).

- **For RAM2 (Address Range 0x100 - 0x17F):**
  - Connect A8 to the Chip Select (CS2) of RAM2.
  - **Logic:** CS2 is active when A8 = 1 (indicating addresses 0x100 - 0x17F).

### Conclusion

This design allows the 8051 microcontroller to interface with two external RAM chips, providing an extended memory capacity beyond its internal RAM. This configuration is crucial for applications requiring more data storage and manipulation capabilities.

You can create this diagram using software like Fritzing, KiCad, or even on paper for clarity. If you have any questions or need further details on any specific part, feel free to ask!

Answer 2

To interface two 2k × 8 RAM chips to an 8051 microcontroller, you need to design a memory system that allows the microcontroller to access these RAM chips. Here’s a step-by-step approach to how this can be done, including the diagram and memory map.

### 1. Understanding the RAM Chips

- **RAM Chip Specification**: Each RAM chip is 2k × 8 bits. This means each chip has 2 kilobytes of memory, and each byte is 8 bits.
- **Addressing**: Each RAM chip will require an address range to be accessed. With 2k memory, each chip has \(2^{11}\) = 2048 locations (bytes).

### 2. 8051 Microcontroller Memory Addressing

The 8051 microcontroller has a 16-bit address bus, which can address up to \(2^{16}\) = 64KB of memory. This means that the microcontroller can address up to 64KB of memory, but in practice, the 8051 typically uses 64KB for both program memory and data memory.

### 3. Interfacing the RAM Chips

To interface the RAM chips, follow these steps:

#### a. **Chip Enable (CE) Pins**: Each RAM chip has a Chip Enable (CE) pin that needs to be controlled to enable the RAM chip for read/write operations.

#### b. **Address Lines**: The address lines from the microcontroller will need to be connected to the RAM chips. Since each RAM chip is 2k × 8, the lower 11 address lines (A0 to A10) will be used to address the memory within the chip. The higher address lines will determine which chip is selected.

#### c. **Data Lines**: The 8 data lines (D0 to D7) from the 8051 microcontroller will connect to the data pins of both RAM chips. Both RAM chips share the same data bus.

#### d. **Address Decoding**: To select which RAM chip is active, you need to use address decoding. Typically, this is done with a combination of address lines and a decoder circuit.

### 4. Memory Map

Here's how the memory map would look for the RAM chips:

- **RAM Chip 1**: 0000H to 07FFH
- **RAM Chip 2**: 0800H to 0FFFH

### 5. Diagram

Here is a textual representation of the interfacing diagram:

```
          +------------------+
          |     8051 MCU     |
          |                  |
    A0-A10 |------------------|---+-----+-----> To RAM Chip Address Lines
          |                  |   |     |
    A11    |------------------|   |     |
          |                  |   |     |
    D0-D7  |------------------|---|-----|-----> To RAM Data Lines
          |                  |   |     |
   /WR     |------------------|   |     |
   /RD     |------------------|   |     |
          +------------------+   |     |
                                  |     |
                                  |     |
            +-----------+     +--|-----|--+     +-----------+
            |  RAM Chip 1|     |  RAM Chip 2 |     | Address  |
            | (2k × 8)   |     | (2k × 8)   |     | Decoder  |
            +-----------+     +-----------+     +-----------+
              |                     |
              |                     |
              |_____________________|
```

### Summary

- **RAM Chip 1** will be accessed from addresses 0000H to 07FFH.
- **RAM Chip 2** will be accessed from addresses 0800H to 0FFFH.
- **Address Lines**: Use A0-A10 to select locations within the chip, and A11 to select the chip.
- **Data Lines**: Connect directly to both RAM chips.
- **Address Decoder**: Use A11 to determine which RAM chip is enabled.

The address decoding can be done using a simple logic circuit or a decoder IC to ensure that each RAM chip is enabled at the appropriate address range.