SEMJUL08 - LECT12 - MEMORY INTERFACING COMPLETED2

SEMJUL08 - LECT12 - MEMORY INTERFACING COMPLETED2 - Memory...

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Unformatted text preview: Memory Interfacing ECE 511: Digital System & Microprocessor What we will learn in this session: Review several important aspects of memory access. Types of memory. How to design a Memory Address Decoder: Full addressing. Partial addressing. Using 74LS138 and 74LS139 decoders. M68k & Memory M68k & Memory M68k has limited space to store data & instructions: 8 x Data registers. 1 x Instruction Register. Not enough for practical applications. Memory expands storage space: 16 MB maximum space. Stores instructions & data. M68k & Memory M68k has 24-bit (23 + 1) address bus: Can address 2 24 locations. 16,777,216 locations (16 MB). Can store much more data, instructions. CLK DTACK HALT RESET VPA BERR VMA E FC FC 1 FC 2 LDS R/W UDS AS A 1-A 23 D-D 15 IPL BR BG BGACK IPL 2 IPL 1 +5V GND GND V CC V CC 68000 Processor Status 6800 Peripheral Control System Control Data Bus Address Bus Asynchronous Bus Control Bus Arbitration Control Interrupt Control *A 0 is used inside 68k AS Address Strobe Purpose: Indicates that M68k is exclusively using system bus . Activated when M68k wants to use system bus: Reading from memory. Writing to memory. Access peripherals. R/W Used to specify read/write operation. 1 pin, output. Three states: High (1): read (default). Low (0): write. DTACK Data Transfer Acknowledge Indicates device ready to begin data transfer . Generated by external device being accessed. When M68k receives signal, knows data transfer can be started, begins read/write operation. During data transfer, M68k inserts wait states until DTACK is received. UDS/LDS Used to activate correct memory chip during read/write: Data usually stored in pairs of chips. Each chip partially connected to data bus. LDS activates D0 to D7 (odd bytes). UDS activates D8 to D15 (even bytes). How Data is Stored in Memory $000000 $000001 $000002 $000003 $000004 $000005 $FFFFFF $FFFFFE $000000 $000002 $000004 $000006 (even addresses) $FFFFFE $000001 $000003 $000005 $000007 (odd addresses) $FFFFFF Chip #1 Chip #2 Controlled by UDS. Controlled by LDS. How Data is Stored in Memory MOVE.L #$12345678,$1000 1 2 3 4 5 6 7 8 $1000 $12 $1002 $56 $1004 $1006 $1006 $1006 $1001 $34 $1003 $78 $1005 $1007 $1009 $100A Chip #1 Chip #2 * Controlled by UDS * Controlled by LDS How Data is Stored in Memory $000000 $000001 $000002 $000003 $000004 $000005 $001FFF $001FFE $000000 $000002 $000004 $000006 $000FFE $000001 $000003 $000005 $000007 $000FFF Chip #1 Chip #2 Controlled by UDS. Controlled by LDS. EVEN ODD $001000 $001002 $001004 $001006 $001FFE $001001 $001003 $001005 $001007 $001FFF Chip #3 Chip #4 EVEN ODD Which one gets selected?...
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This note was uploaded on 11/17/2011 for the course MCT 3235 taught by Professor Dr during the Spring '11 term at International Islamic University Malaysia.

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SEMJUL08 - LECT12 - MEMORY INTERFACING COMPLETED2 - Memory...

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