Circuit Diagram

Circuit Diagram


Dodo requires a connection to a host computer in order to flash games onto the cartridges and to update the system firmware on the EEPROM. That connection is RS-232. RS-232 connectivity is provided by the 65C51 communication adapter, and the MAX202CPE in order to convert the TTL logic levels of the 65C51 to RS-232. A few external components are necessary. The 1.8342mhz oscillator feeds the internal baud rate generator inside of the 65C51, and a number of capacitors provide the charge pump for the MAX202 that needs to scale to higher voltages.

65C51 Pin Descriptions

Pin(s) Discription
TxD Transmit line, connected to MAX202CPE
RxD Receive line, connected to MAX202CPE
XTL0 Unconnected because bare crystal not used
XTL1 Connected to the 1.8432 oscillator
RxC Unconnected
RS0, RS1 Register address lines. Connected to A0 - A1. Chip select is generated based on the other address lines, least significan 2 bits determine register.
Data D0 - D7 data bus
CS1B Chip Select 1, connected to the 65C51 select generated by the glue logic
CS0 Chip select 0. Tied High, not needed
RWB Read/Write Connected to RW from the processor
IRQB Interrupt line, connected to IRQ of processor
RESB Connected to the Reset line
PHI2 Connected to the 1mhz oscillator
DSRB Unused. Tied to GND
DCDB Unused. Tied to GND
DTRB Unconnected
RTSB Control line connected to MAX202CPE
CTSB Control line connected to MAX202CPE


Component Description Image
65C51 Asynchronous Communications Interface Adapter Image
MAX202CPE RS-232 interface Image
1.8342mhz oscillator Oscillator for the buad rate generator Image
DB9 connector RS-232 connector Image
0.1uF Capacitors Charge pump capacitors Image