15. memory interfacing i
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This document discusses memory interfacing in microprocessors. It explains that memory stores binary instructions using registers made of flip-flops as basic storage elements. Tri-state devices have three states - logic 1, 0, and high impedance. A tri-state buffer can be used as a memory cell by enabling the input buffer to write and output buffer to read using active low signals. Four latches can form a 4-bit register where a specific register is enabled using a 2-to-4 decoder and address lines A0 and A1 to write or read from that register.
15. memory interfacing i
- 1. MICROPROCESSOR 8085 LECTURE 18 MEMORY INTERFACING-I PROF. SANDIP DAS
- 2. WHAT IS MEMORY • It stores binary instruction • Broadly classified as RAM and ROM • Made of registers and each register has a group of flip-flops. So, we infer that a latch or a flip-flop acts as the basic storage element that can store bits. Basic Latch D Q EN DIN EN D Q ENEN Dout DIN 𝑊𝑅 𝑅𝐷 Dout Latch with Tri-state buffer
- 3. TRI-STATE DEVICES • Tri-state logic devices have three stages: logic 1, logic 0 and high impedance. Enable Enable Active High Active Low Tri-State Inverter with active High Enable line Tri-State Inverter with active Low Enable lines Buffer A Tri-state Buffer Enable Active Low
- 4. LATCH WITH A TRI-STATE BUFFER AS A MEMORY CELL • We can write into latch by enabling input buffer by providing active low signal • We can read from the latch by enabling the output buffer by providing active low signal D Q ENEN DIN 𝑊𝑅 𝑅𝐷 Dout 𝑊𝑅 𝑅𝐷
- 5. FOUR LATCHES AS FOUR BIT REGISTER
- 6. TO WRITE INTO OR READ FROM ANY ONE OF THE REGISTERS: SPECIFIC REGISTER SHOULD BE ENABLED Register 3 Register 2 Register 1 Register 0 Output Buffer Input Buffer 2-t0-4 Decoder𝑊𝑅 𝑅𝐷 A1 A0 • Thus, 2-to-4 decoder can perform the required function with the use of two input lines A0 and A1. • These two input lines can have four different bit combinations (00,01,10,11) and each combination can enable one of the registers namely Register 0 to Register 3. • Thus, the Enable signal of the flip-flops is replaced by two address lines. outputs inputs