# ULX3S PCB

This is work-in-progress place for putting
some wishes of a small (94x51 mm) FPGA board.

ULX3S = University digital logic Learning eXtensible
board release 3 with SDRAM, Successor of ULX2S.

    kicad ulx3s.pro

[Schematics](/doc/schematics.pdf) is mostly complete.
PCB routing is mostly complete too.

3D preview

![TOP](/pic/ulx3st.jpg)
![BOTTOM](/pic/ulx3sb.jpg)

# Features

FPGA: Lattice ECP5 LFE5U-25F-6BG381C

USB: FTDI FT231XS (1Mbit JTAG and 3Mbit usbserial)

GPIO: All differential, PMOD-friendly

RAM: 32MB SDRAM MT48LC16M16

Flash: 8MB SPI flash S25FL164 for FPGA config

Storage: Micro-SD slot

LEDs: 10 (8 blink-LEDs, 2 USB leds)

Buttons: 7 (4 direction, 2 fire, 1 power button)

Audio: 3.5 mm stereo jack

Video: GPDI connector with 3.3V-5V I2C bidirectional level shifter

Display: placeholder for 0.96-1.3" SPI OLED COLOR or B/W

WiFi+bluetooth: placeholder for ESP-32 (JTAG and serial over WiFi possible)

ADC: 8 channels, 12 bit, 1 MSa/s MAX11123

Power: 3 Switching voltage regulators: 1.2V, 2.5V, 3.3V

Clock: 25 MHz onboard, external differential clock input

Low power sleep: RTC clock wakeup, power button, 32768 Hz quartz and battery


GPDI is General Purpose Differential Interface,
Electrically LVDS, mostly TMDS tolerant
female receptacle more-or-less compatible
with digital monitors/TVs


# Todo

Make the prototype.

    [x] Silkscreen Double outline for BGA chip
    [x] Silkscreen do not write over the solder pads
    [ ] Silkscreen BGA names on ESP32 placeholder and 2.54 mm headers
    [x] Silkscreen JTAG signal names on 6-pin 2.54 mm header
    [x] Silkscreen remove OLED outline
    [x] Solder stop mask must go inbetween all SMD chip pads
    [x] External differential clock input at J1_33 +/-
    [ ] Thinner copper, more spacing to SDRAM-FPGA
    [x] physically sprinkle VCC blocator capacitors under BGA
    [ ] Values on silkscreen
    [x] Dedicated antenna pin
    [x] onboard 433 antenna
    [ ] 433 remove GND and silkscreen test point
    [x] Resistors for LEDs
    [x] Move USB LEDs from bottom to top side
    [ ] Improve SDRAM routing - use VIAs for closest pins
    [x] Increase thickness of power lines (5V, 3.3V, 2.5V)
    [x] Compile a f32c bitstream using the schematics
    [x] Compile differential GPDI output
    [x] Connect more lines from ESP-32 to FPGA
    [x] Connect FPGA USB D+/D- with 1.5k pullup in USB 1.1 (full speed) mode
    [x] FPGA USB add 27 ohm + 3.6 V zener
    [x] Symmetrically place USB connectors left-right 
    [ ] Jumpers to switch 2.5V/3.3V for left IO banks
    [x] External JTAG header
    [x] Move JTAG 2 mm left
    [ ] Move WiFi Disable jumper above the buttons
    [x] Sprinkle 2.2uF capacitors on power lines
    [x] Spice simulation of power-up/shutdown network
    [x] 27ohm D+/D- to FT231XS
    [x] DIP switch (4 switches)
    [x] MAX11123 ADC SPI
    [x] I2C for RTC
    [x] main usb connector on top side 
    [ ] space screw to other parts
    [x] move battery away from screw hole
    [x] top layer GND fill
    [x] R25 move away from oled screw hole
    [ ] board cut off nothches inisde for space saving
    [x] DIP switch to the right near RAM
    [x] Move HDMI a bit closer to OLED
    [x] 32768Hz oscillator footprint
    [x] SD card footprint SCHD3A0100
    [ ] SD use CD (card detect) contacts
    [x] move USB 0.5-1mm more out
    [x] DIP SW footprint correct
    [x] AUDIO jack footprint fits
    [ ] AUDIO jack pin 4 not connected
    [x] BTN footprint too small
    [x] SMPS jumpers default OFF for prototype testing
    [x] FPGA DONE to ESP-32
    [x] Diodes manual soldering
    [ ] for easier FT231XS rev A,B,C workaround by tying
        Connect pin 18 CBUS0 (TXDEN) FTDI with unplaced resistor to GND
        See TN140_FT231X Errata