A trip down memory lane
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Transcript of A trip down memory lane
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RAM and the Apple II
• Static and Dynamic types
• Static RAM an array of flip-flops (latches)
• Dynamic RAM an array of capacitors
• SRAM faster, less dense, more power
• DRAM denser, slower, requires refresh
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RAM and the Apple II
• Supported two types of DRAM chip
• 3 banks of 8 chips
• 4kbit or 16kbit DRAMs for a total of 48k
Original Apple II/II+
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RAM and the Apple IIApple II memory map
48k
I/O
ROM
$0000
$BFFF$C000
$CFFF
$D000
$FFFF
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RAM and the Apple II
• Designed for Apple Pascal
• Adds 16k more RAM
• Bank switched to overlay ROM area
The Language System
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RAM and the Apple II
RAM48k
I/O
ROM12k
$0000
$BFFF$C000
$CFFF
$D000
$FFFF
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
Overlays ROM
16k Language Card
Motherboard RAM and ROM
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RAM and the Apple II
• Saturn Systems 64k and 128k Cards
• Just like having 4 or 8 Language Cards
• Register controls which is active
Third Party Extensions
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RAM and the Apple IIe
• RAM gets cheaper, move to 64k DRAM
• Language Card built in
• Optional Auxiliary 64k RAM
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RAM and the Apple IIe
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
RAM48k
I/O
$0000
$BFFF$C000
$CFFF
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
RAM48k
I/O
$0000
$BFFF$C000
$CFFF
Main Memory Auxiliary Memory
Switches with zero page
Switchable reads and writes
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RAM and the Apple IIe
• Multibank Auxiliary Cards Appear
• 256k DRAM becomes affordable
• Applied Engineering RAMWorks
Third Party Extensions
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The RamWorks Card
• Bank Select Register allows 256 banks
• (in theory) 16MB is possible
• 1MB of RAM on Board
• Daughter Cards allow extension to 3MB
• RGB video and 65816 processor options
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The RamWorks Card
• Can be used as RamDisk
• Extends the AppleWorks Desktop
• Print buffering
• Most “power” applications can use it
• Adds real RAM
Advantages
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The RamWorks Card
• Apple went another way (Slinky)
• Tricky to program for
• Getting hard to find
• Extender cards unobtainium
• Only really useful for programmers
Disadvantages
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Alternatives
• Apple II Memory Expansion Card (Slinky)
• Provides extra RAM as secondary storage
• Essentially a RAMDisk card
• Can’t directly address the RAM
• Somewhat pointless when fast secondary storage available.
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Today
• Can we recreate the RamWorks ?
• DRAM or SRAM ?
• Just how much RAM can we add ?
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SRAM
• Cypress CY62167ELL-45ZXI
• Can run at 5V
• 16mbit configurable as 2mb x 8
• TSOP-48 package
• 2.2mA at 1Mhz
• Affordable
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Auxiliary Slot
• Address bus multiplexed
• Borrows motherboard RAM refresh
• No access to IO areas
• C07x strobe is available
• Other signals for video expansion
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SRAM Card
AUXSlot
MultiplexedAddress Bus
AddressDeMux
Data Bus
BankSelect
Register
Decoded 24 bitAddress
Video Data Bus
StaticRAM
Upper 8 bits of address disabled during video fetch (PH1)
Upper 8 bits of address enabled during CPU fetch (PH0)
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SRAM Card
• 7400 series logic all we need
• 74HCT simplifies design
• Test socket for SRAM
• Only 8 chips required
• Easily assembled on a Breadboard
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ScramWorks I
• Static RAM
• CMOS Design
• Replaces RamWorks
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The Future
• Prototype PCB
• More testing
• Does anyone want one ?
• Replicate RamWorks daughtercard ports ?
• Possible move to low voltage large SRAMs
• BGA tough to work with
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Questions ?
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