1. It’s Game Time
Matt Jenkins <mdj@emdeejay.net>
OzKFest April 2015

2. ScramWorks
• Design has evolved to higher capacity SRAM
• 1 or 2 chips for 8MB or 16MB capacity
• 3.3V circuitry
• 100% RamWorks compatibility
• AE and Nishida Radio video connectors
• Soon, and with brothers

3. Serial Segue
• Communicates between computer systems
• Or between parts within a computer system
• Increasing replacing parallel communications
• USB
• Serial ATA
• PCI-e slots are serial busses

4. Serial Style
• Asynchronous
• Rely on accurate timing on each end point
• Synchronous
• Clock is provided on the bus
• Flow Control
• In band
• Out of band

5. Serial - RS232
• Super Serial Card, Apple IIc, 6551 ACIA
• Asynchronous
• In band and out of band flow control
• XON/XOFF, RTS/CTS
• Logic level and line level.
• 115,200Kbps to many megabits

6. Serial - intercomponent
• Widely used in Arduino
• RTC, Stepper Motor, GPIO, Servo
• i2c
• SPI
• 1-wire

7. i2c
• Inter-Integrated Circuit
• 2-wire, synchronous, half-duplex
• 10Khz, 100Khz, 400Khz modes
• Open-drain
• Multi-master capable

8. i2c
• Data line - SDA
• Clock line - SCL
• Master drives clock
• All devices share data line
• Actual speed can be variable (0-100Khz)

9. i2c
(Image from Wikipedia)

10. Apple II - i2c ?
• Can it be done ?
• i2c allows slower speeds
• Ought to be easy!
• Where do we plug it in ?

11. Apple II Game Port
• 4 Annunciator outputs
• 3 Pushbutton inputs
• 4 Paddle Inputs
• 1 Utility Strobe

12. Apple II Game Port

13. Apple II Game Port
• Inputs and outputs are TTL
• But i2c is open drain
• Going to need some electronics!

14. Emitter Follower

15. Open Drain

16. Apple i2c - Schematic
• Two MOSFETs
• Two Resistors
• Two sets required to do both SDA and SCL

17. Apple i2c - SDA schematic
1243774

18. Apple i2c - Code
• Some simple assembly language
• Merlin 8/16 (32?)
• Macros should help
• Ampersand extensions for Applesoft

19. Apple i2c - Code
AN0OFF EQU $C058
AN0ON EQU $C059
AN1OFF EQU $C05A
AN1ON EQU $C05B
PB0 EQU $C061
PB1 EQU $C062
PB2 EQU $C063

20. Apple i2c - Code
SDAOFF MAC
BIT AN0ON
<<<
SDAON MAC
BIT AN0OFF
<<<
SCLOFF MAC
BIT AN1ON
<<<
SCLON MAC
BIT AN1OFF
<<<

21. Apple i2c - Code
SCLSTAT MAC
LDA PB1
<<<
SCLWAIT MAC
WAIT SCLSTAT
BMI WAIT
NOP
<<<
I2CSTART MAC
SDAOFF
NOP
NOP
NOP
NOP
SCLOFF
<<<
I2CCLOCK MAC
SCLON
NOP
NOP
SCLOFF
NOP
<<<

22. Summary
• Not working yet (sorry!)
• Questions ?