RASPI-PLUS-GVS-CFG

Features

• All Raspberry Pi I/O lines
• 8-bit bidirectional 3.3V to 5V level translator
• Configuration EEPROM
• Fuses on power

Raspberry Pi I/O lines

• All of the Raspberry Pi Model B+ I/O connections are brought to GVS connectors. This is:
  • (17) GPIO lines on GVS connectors
  • (2) SPI interfaces
  • (1) UART interface
  • (1) I2C interface

Level translators

• The BBB-GVS board use an 8-bit wide Texas Instrument TXS0108 voltage translator to convert up to 8 of the 3.3V I/O lines to 5V I/O levels.

Voltage Translators Features

• No Direction-Control Signal Needed
• Max Data Rates
  • 60 Mbps (Push Pull)
  • 2 Mbps (Open Drain)
• 1.2 V to 3.6 V on A Port and 1.65 V to 5.5 V on
• B Port (VCCA ≤ VCCB)
• No Power-Supply Sequencing Required –
  • Either VCCA or VCCB Can Be Ramped First
• Latch-Up Performance Exceeds 100 mA Per JESD 78, Class II
• ESD Protection Exceeds JESD 22 (A Port)
  • 2000-V Human-Body Model (A114-B)
  • 150-V Machine Model (A115-A)
  • 1000-V Charged-Device Model (C101)
• IEC 61000-4-2 ESD (B Port)
  • ±6-kV Air-Gap Discharge
  • ±8-kV Contact Discharge

Voltage Translators Architecture

Datasheet

The TXS0108E can be used in level-translation applications for interfacing devices or systems operating at different interface voltages with one another. The TXS0108E is ideal for use in applications where an open-drain driver is connected to the data I/Os. The TXS0108E can also be used in applications where a push-pull driver is connected to the data I/Os, but the TXB0104 might be a better option for such push-pull applications. The TXS0108E device is a semi-buffered auto-direction-sensing voltage translator design is optimized for translation applications (e.g. MMC Card Interfaces) that require the system to start out in a low-speed open-drain mode and then switch to a higher speed push-pull mode.

To address these application requirements, a semi-buffered architecture design is used and is illustrated above (see Figure 1). Edge-rate accelerator circuitry (for both the high-to-low and low-to-high edges), a High-Ron n-channel pass-gate transistor (on the order of 300 Ω to 500 Ω) and pull-up resistors (to provide DC-bias and drive capabilities) are included to realize this solution. A direction-control signal (to control the direction of data flow from A to B or from B to A) is not needed. The resulting implementation supports both low-speed open-drain operation as well as high-speed push-pull operation.

When transmitting data from A to B ports, during a rising edge the One-Shot (OS3) turns on the PMOS transistor (P2) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from A to B, the One-Shot (OS4) turns on NMOS transistor (N2) for a short-duration and this speeds up the high-to-low transition. The B-port edge-rate accelerator consists of one-shots OS3 and OS4, Transistors P2 and N2 and serves to rapidly force the B port high or low when a corresponding transition is detected on the A port.

When transmitting data from B to A ports, during a rising edge the One-Shot (OS1) turns on the PMOS transistor (P1) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from B to A, the One-Shot (OS2) turns on NMOS transistor (N1) for a short-duration and this speeds up the high-to-low transition. The A-port edge-rate accelerator consists of one-shots OS1 and OS2, Transistors P1 and N1 components and form the edge-rate accelerator and serves to rapidly force the A port high or low when a corresponding transition is detected on the B port.

Fuses

• The board has Resettable fuses on the 3.3V and 5V from the Raspberry Pi.
• These fuses protect your Raspberry Pi from overloads.
• These fuses are 1/2 Amp PTC fuses.
• PTC fuses have certain advantages (they are self healing) and disadvantages (they are not like a wire fuse which acts like a switch).
• If you trust your wiring you may choose to solder a wire over the fuse.
  • Care should be taken when doing so.

Configuration EEPROM

• The card has a Raspberry Pi Model B+ configuration EEPROM.

3.3V Connectors

The following are all 3.3VDC connections.

Raspberry Pi B Plus GPIO Connector

• J8 on the Pi.

I2C bus

1. GND
2. 3.3V
3. SDA
4. SCL

UART I/F

1. GND
2. 3.3V
3. TxD
4. RxD

IO_4 GVS

1. GND
2. 3.3V
3. GPIO_4

IO_18 GVS

1. GND
2. 3.3V
3. GPIO_18

IO_17 GVS

1. GND
2. 3.3V
3. GPIO_17

IO_27 GVS

1. GND
2. 3.3V
3. GPIO_27

IO_23 GVS

1. GND
2. 3.3V
3. GPIO_23

IO_22 GVS

1. GND
2. 3.3V
3. GPIO_22

IO_24 GVS

1. GND
2. 3.3V
3. GPIO_24

IO_25 GVS

1. GND
2. 3.3V
3. GPIO_25

SPI0 (Serial Peripheral Interface)

1. GND
2. 3.3V
3. MOSI
4. MISO
5. SCK
6. CE0

SPI1 (Serial Peripheral Interface)

1. GND
2. 3.3V
3. MOSI
4. MISO
5. SCK
6. CE1

IO_5 GVS

1. GND
2. 3.3V
3. GPIO_5

IO_6 GVS

1. GND
2. 3.3V
3. GPIO_6

IO_12 GVS

1. GND
2. 3.3V
3. GPIO_12

IO_13 GVS

1. GND
2. 3.3V
3. GPIO_13

IO_19 GVS

1. GND
2. 3.3V
3. GPIO_19

IO_16 GVS

1. GND
2. 3.3V
3. GPIO_16

IO_26 GVS

1. GND
2. 3.3V
3. GPIO_26

IO_20 GVS

1. GND
2. 3.3V
3. GPIO_20

IO_21 GVS

1. GND
2. 3.3V
3. GPIO_21

J22 - EEPROM Address/Write Enable Header - Rev X2 Hat

• Write Enable - Install header to allow writes to EEPROM
• Remove header to protect EEPROM contents from accidental writes

J22 - EEPROM Address/Write Enable Header - Rev X1 Hat

• 1-2 = Write Enable - install to allow writes
• 3-4 = A0 - installed = 0
• 5-6 = A1 - installed = 0
• 7-8 = A2 - installed = 0

J23 - Voltage translator, 3V side

• V3-1 = Bit 1
• V3-2 = Bit 2
• V3-3 = Bit 3
• V3-4 = Bit 4
• V3-5 = Bit 5
• V3-6 = Bit 6
• V3-7 = Bit 7
• V3-8 = Bit 8

5V Connectors

The following are 5V connectors.

V5-1 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit1

V5-2 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit2

V5-3 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit3

V5-4 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit4

V5-5 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit5

V5-6 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit6

V5-7 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit7

V5-8 - GVS connector, 5V side

1. Ground
2. +5V
3. Bit8

Layout - Rev X2

Kickstarter Edition

Layout - Rev X1

Prototype Edition - Not available on Kickstarter

RasPi-GVS-Plus-CFG-mechs.png

Assembly Sheet

RasPi-Plus-GVS-Cfg Configuration Sheet - Rev X2

Design Validation Testing - Rev X1 Board

RASPI-PLUS-GVS-CFG DVT

Factory Acceptance Tests (FAT)

Hardware

• FAT requires the following:
• Raspberry Pi Model B+ or equivalent (RasPi)
• Power supply for Raspberry Pi (5V at 1 Amp min) with Micro USB connector
• Monitor, Keyboard or Ethernet cable and laptop running puTTY
• Test Software loaded onto RasPi
• (1) LED-Test card
• + side of LEDs to V5-2 thru 8
• - side of LEDs to GND at +5V side
• Jumpers (female-to-female)
• Daisy-chain cables
  • 8-pin, 1-2, 3-4, 5-6, 7-8 @ IO6-IO21
  • (2) 4-pin, 1 open, 2 open, 3-4 @ J1, J2
• Single female to female @ SPI1-IO5
• 6 pin, 1 open, 2 open, 3-4, 5-6 @ SPI0
• (3) 8-pin female-female jumper cables
• 1 jumper +3.3V side to IO4-IO25
• 2 (to LED-Test card)
• Unit Under Test (UUT)

Preliminary

• Install UUT onto RasPi
• Install Cables
• Power up card
• Log into RasPi

GVS Connector - Daisy-chain Tests

• On RasPi console:

pi
raspberry
 
cd ~/RasPi/RasPi-Plus-GVS-Cfg/
sudo python fastTests.py
 

• Result should be

Daisy test passed

• LEDs should cycle

I2C

cd ~/RasPi/RasPi-Plus-GVS-Cfg/eeprom/
sudo ./eep2flash.sh -w -t=24c32 -f=eepcfg.eep
sudo ./eep2flash.sh -r -t=24c32 -f=myeep.eep 
rm stuff.eep
./eepdump myeep.eep stuff.eep 
more stuff.eep | grep vendor
 
Verify:
# ---------- Dump generated by eepdump handling format version 0x01 ----------
#
# --Header--
# signature=0x69502d52
# version=0x01
# reserved=0
# numatoms=2
# eeplen=117
# ----------


# Start of atom #0 of type 0x0001 and length 57
# Vendor info
product_uuid 3ea7c89f-353e-4633-bd6c-2572996f277b
product_id 0x0004
product_ver 0x0001
vendor "land-boards.com"   # length=15
product "RASPI-PLUS-GVS-CFG"   # length=18
# End of atom. CRC16=0x437a


# Start of atom #1 of type 0x0002 and length 32
# GPIO map info
gpio_drive 0
gpio_slew 0
gpio_hysteresis 0
back_power 0
#        GPIO  FUNCTION  PULL
#        ----  --------  ----
# End of atom. CRC16=0x6eed

• Combined copy/paste

cd ~/RasPi/RasPi-Plus-GVS-Cfg/eeprom/
sudo ./eep2flash.sh -w -t=24c32 -f=eepcfg.eep
sudo ./eep2flash.sh -r -t=24c32 -f=myeep.eep 
rm stuff.eep
./eepdump myeep.eep stuff.eep 
diff stuff.eep eepcomp.eep
cd ~/RasPi/RasPi-Plus-GVS-Cfg/
sudo python fastTests.py== Schematic ==

Drivers/Example Code
* Github repo - Driver code

Assembly Sheet
* RASPI-PLUS-GVS-CFG Assembly Sheet