tang_nano_9k_vic20_lcd

VIC20 living in a Gowin GW1NR-9 FPGA on a Sipeed Tang Nano 9k.

Video output is adapted for a 5" TFT-LCD module 800x480 Type SH500Q01Z (Ilitek ILI6122)

Original VIC-20 core by MikeJ (Mike Johnson) and T65 WoS (Wolfgang Scherr)

Features

• TFT-LCD Video Output
• Speaker Sound
• PS/2 Keyboard
• Joystick

By default cartridge ROM will be booted (see push button how to suppress).

VIC-20 in a FPGA

Tang Push Button utilization

• S1 push button Reset
• S2 Cartridge ROM disable (keep S2 pressed while power-on or excert a S1 push-button Reset, release after)

Powering

Prototype circuit with Keyboard and Audio Amp can be powered by Tang USB-C connector from PC or a Power Supply Adapter.

Synthesis

Source code can be synthesized, fitted and programmed with GOWIN IDE Windows or Linux.

Simulation

Basic testbench as a starting point in the TB folder (vic20_tb.vhd)
Script for compiling the Gowin library, sources and testbench in the simulation folder (sim_vic20.do).
For Simulation run execute_simulation.bat (Windows) or execute_simulation.sh (Linux)

GOWIN IP Blocks

For sake of simplification i use block SRAM resources for all memories (SP, SDP, pROM). In addition rPLL, CLK divdiers and GSR resource.

Pin mapping

see pin configuration in .cst configuration file

cartride ROM

The bin2mi tool can be used to generate from a 8192 byte Game ROM new pROM VHDL code. For the ROM image i took had to remove the first byte in the generated HEX file indicating the VIC-20 ROM region (0xA0) before providing needed Memory initialization file to the IP Block generator.

HW circuit considerations

• PS/2 keyboard has to be connected to 3.3V tolerant FPGA via level shifter to avoid damage of inputs ! Use e.g. 2 pcs SN74LVC1G17DBVR 5V to 3V3 level shifter. My Keyboard has internal pull-up resistors to 5V for Clock and Data Signals so didn't needed external ones.
• Joystick interface is 3.3V tolerant. Joystick 5V supply pin has to be left floating !
• The FPGA pin delivering SigmaDelta Audio signal to the Amplifier need a low pass filter. 3K3 series Resistor and 4n7 Capacitor to GND.
• Tang Nano 5V output connected to Audio Amplifier and Keyboard supply. Tang 3V3 output to level shifter supply.

Pinmap D-SUB 9 Joystick Interface

Joystick pin	Tang Nano pin	FPGA pin	Joystick Function
1	J5 8	28	Joy3 RIGHT
2	J5 7	27	Joy2 LEFT
3	J5 6	26	Joy1 DOWN
4	J5 5	25	Joy0 UP
5	n.c.	n.c.	POT Y
6	J5 9	29	FIRE B.
7	n.c.	n.c.	5V
8	J6 23	-	GND
9	n.c.	n.c.	POT X

Pinmap PS/2 Interface

PS/2 pin	Tang Nano pin	FPGA pin	PS2 Function
1	J6 10	77	DATA
2	n.c.	-	n.c.
3	J6 23	-	GND
4	J6 18	-	+5V
5	J6 11	76	CLK
6	n.c.	-	n.c

low pass filter for Audio Amplifier input

BOM

Sipeed Tang Nano 9k
SH500Q01Z LCD-TFT (Ilitek ILI6122)
D-SUB 9 M connector
Commodore/Atari compatible Joystick
or alternatively 5D Rocker Joystick navigation button module
3K3 Resistor
4n7 Ceramics
Mini PAM8403 Audio Amplifier Module
8R Speaker
PS/2 Keyboard
PS/2 Socket Adapter Module
2 pcs SN74LVC1G17DBVR level shifter
Prototype Board