Gfe Mayur Vihar Call Girls Service WhatsApp -> 9999965857 Available 24x7 ^ De...
address decoding.pdf
1. Addressing Memory and Ports
Reference: Microprocessors and
Interfacing – Douglas V Hall – Chapter 7
2. Address Decoder
• 3to8 decoders like 74LS138 serve as the
address decoders.
• Produces a signal which enables the ROM,
RAM, or port device, which is enabled for a
particular address
• Makes sure that only one device is enabled at
a time to put data in the bus.
7. Memory Mapped I/O
• Using a decoder which translates memory
addressing to chip select signals for port
device is called Port Decoder
• Advantage: Any instruction that references
memory, can be used to input data from or
output data to ports
• Disadvantage: Some of the system memory
space is used up
9. Memory Bank
• Odd-even memory bank is used to read or
write 16 bit at a time
• Address A1-A19 are used to select desired
memory within the bank
• A0 is used for selecting lower bank and Bus
High Enable is used for selecting upper bank
• It also prevents unwanted writing of data in
adjacent memory location during byte
operation
10. Addressing Decoding
Type Address Data Type BHE A0 Bus Cycles
Data lines
used
Even 0000 Byte 1 0 One D0-D7
Even 0000 Word 0 0 One D0-D15
Odd 0001 Byte 0 1 One D8-D15
Odd 0001 Word 0 1 First D8-D15
1 0 Second D0-D7