A Trip Down Memory Lane

Matt Jenkins <mdj@emdeejay.net>

Monday, 29 July 13

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

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

RAM and the Apple IIApple II memory map

48k

I/O

ROM

$0000

$BFFF$C000

$CFFF

$D000

$FFFF

Monday, 29 July 13

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

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

Monday, 29 July 13

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

RAM and the Apple IIe

• RAM gets cheaper, move to 64k DRAM

• Language Card built in

• Optional Auxiliary 64k RAM

Monday, 29 July 13

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

Monday, 29 July 13

RAM and the Apple IIe

• Multibank Auxiliary Cards Appear

• 256k DRAM becomes affordable

• Applied Engineering RAMWorks

Third Party Extensions

Monday, 29 July 13

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

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

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

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

Today

• Can we recreate the RamWorks ?

• DRAM or SRAM ?

• Just how much RAM can we add ?

Monday, 29 July 13

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

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

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)

Monday, 29 July 13

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

ScramWorks I

• Static RAM

• CMOS Design

• Replaces RamWorks

Monday, 29 July 13

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

Questions ?

Monday, 29 July 13