Circuit Diagrams

Schematic

The Issue 2B (rev 1) schematic can be downloaded here.

The thee tail matrix keyboard schematic can be downloaded here.

J13 - Daughter board connector

J15 - Next GPIO

CN5 - Expansion bus (edge connector)

J10/J11 - Memory Expansion Ports

J4/J7 J8/J14 - Joystick Ports

CN1 - VGA Video Port

Notes:

• In VGA mode (scandoubler enabled), H-SYNC and V-SYNC are carried separately on their respective pins.
• In RGB mode (scandoubler disabled), H-SYNC carries composite sync, and V-SYNC carries 1.
• Pin 14 carries 3V3, which can be connected to SCART pin 16 to indicate RGB to the display.
• There is no convenient source of voltages between 9.5-12V to indicate 4:3 aspect ratio to the display on SCART pin 8, so this is usually left unconnected.

CN8 - Digital Port

CN2/CN6/CN7 - SD Reader (Mainboard) (CN6 on reverse)

CN10/CN11/CN12 - SD Reader (Daughterboard) (CN12 on reverse)

Accelerator Board

Real Time Clock (RTC)

CN9 - ESP8266-01/RS-232 Port