Slides from the presentation of my "Scramworks" prototype Ramworks compatible memory card for the Apple IIe

1. A Trip Down
Memory Lane
Matt Jenkins <mdj@emdeejay.net>
Monday, 29 July 13

2. 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
Monday, 29 July 13

3. 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+
Monday, 29 July 13

4. RAM and the Apple II
Apple II memory map
48k
I/O
ROM
$0000
$BFFF
$C000
$CFFF
$D000
$FFFF
Monday, 29 July 13

5. RAM and the Apple II
• Designed for Apple Pascal
• Adds 16k more RAM
• Bank switched to overlay ROM area
The Language System
Monday, 29 July 13

6. RAM and the Apple II
RAM
48k
I/O
ROM
12k
$0000
$BFFF
$C000
$CFFF
$D000
$FFFF
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
Overlays ROM
16k Language Card
Motherboard RAM and ROM
Monday, 29 July 13

7. 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
Monday, 29 July 13

8. RAM and the Apple IIe
• RAM gets cheaper, move to 64k DRAM
• Language Card built in
• Optional Auxiliary 64k RAM
Monday, 29 July 13

9. RAM and the Apple IIe
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
RAM
48k
I/O
$0000
$BFFF
$C000
$CFFF
8k
4k Bank4k Bank $D000-$DFFF
$E000
$FFFF
RAM
48k
I/O
$0000
$BFFF
$C000
$CFFF
Main Memory Auxiliary Memory
Switches with zero page
Switchable reads and writes
Monday, 29 July 13

10. RAM and the Apple IIe
• Multibank Auxiliary Cards Appear
• 256k DRAM becomes affordable
• Applied Engineering RAMWorks
Third Party Extensions
Monday, 29 July 13

11. 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
Monday, 29 July 13

12. The RamWorks Card
• Can be used as RamDisk
• Extends the AppleWorks Desktop
• Print buffering
• Most “power” applications can use it
• Adds real RAM
Advantages
Monday, 29 July 13

13. 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
Monday, 29 July 13

14. 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.
Monday, 29 July 13

15. Today
• Can we recreate the RamWorks ?
• DRAM or SRAM ?
• Just how much RAM can we add ?
Monday, 29 July 13

16. SRAM
• Cypress CY62167ELL-45ZXI
• Can run at 5V
• 16mbit configurable as 2mb x 8
• TSOP-48 package
• 2.2mA at 1Mhz
• Affordable
Monday, 29 July 13

17. Auxiliary Slot
• Address bus multiplexed
• Borrows motherboard RAM refresh
• No access to IO areas
• C07x strobe is available
• Other signals for video expansion
Monday, 29 July 13

18. SRAM Card
AUX
Slot
Multiplexed
Address Bus
Address
DeMux
Data Bus
Bank
Select
Register
Decoded 24 bit
Address
Video Data Bus
Static
RAM
Upper 8 bits of address disabled during video fetch (PH1)
Upper 8 bits of address enabled during CPU fetch (PH0)
Monday, 29 July 13

19. SRAM Card
• 7400 series logic all we need
• 74HCT simplifies design
• Test socket for SRAM
• Only 8 chips required
• Easily assembled on a Breadboard
Monday, 29 July 13

20. ScramWorks I
• Static RAM
• CMOS Design
• Replaces RamWorks
Monday, 29 July 13

21. 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
Monday, 29 July 13

22. Questions ?
Monday, 29 July 13