EVK-ANNA-B112 - User Guide
UBX-18018539 - R01
Product description
Page 16 of 29
Conn. Pin
No.
Raspberry
Pi pin
Description
Schematic
net name
nRF52
pin
Alternate functions and notes
30
GND
Ground
GND
GND
31
IO06
Digital I/O
IO_31
P0.26
32
IO12
Digital I/O
IO_30
P0.25
33
IO13
Digital I/O
UART_RTS P0.11
34
GND
Ground
GND
GND
35
IO19
Digital I/O
UART_CTS P0.19
36
IO16
Digital I/O
IO_36
P0.22
37
IO26
Digital I/O
IO_37
P0.23
38
IO20
Digital I/O
IO_38
P0.24
39
GND
Ground
GND
GND
40
IO21
Digital I/O
IO_45
P0.20
Table 10: Pinout of the Raspberry Pi compatible interface
1.8.1
Powering considerations
There are two voltage nets used in the Raspberry Pi interface 3V3_PI and 5V. Both the 3V3_PI and
5V nets can be used to power HATs, but should not be used when connecting to a Raspberry Pi. See
section 1.6.6 for more information.
⚠
The 3V3_PI power net must not be connected to the 3.3 V supply when connected to a Raspberry
Pi board. It could damage both the boards.
1.8.2
UART
The Raspberry Pi interface provides two pins -
IO14 and IO15, which can be used for UART
communications. In UART communications, signals are always connected RX <-> TX and vice versa.
This means that on a Raspberry Pi board
IO14 will be TX and on a HAT it will be RX. To support talking
to both HATs and Pi boards, the zero
Ω
resistors - R57, R58, R59 and R60 can be used to toggle the
ANNA TX and RX pins between
IO14 and IO15. If an ANNA-B112 is used, this switch can also be made
in the software. By default, the EVK-ANNA-B112 will be configured to simulate a HAT, and
IO14 is
connected to the ANNA
UART_RXD pin and IO15 is connected to the ANNA UART_TXD pin
respectively.
1.8.3
EEPROM support
The Raspberry Pi interface supports a unique EEPROM solution to store the HAT specific IO
configurations on the HAT board, to be read by the Raspberry Pi before configuring its IOs. The two
pins used for this are
ID_SD and ID_SC and are connected to the ANNA-B112 module. The
ANNA-B112 module can thus either read the IO configuration from a HAT, or simulate an EEPROM
and send configurations to a connected Pi. This requires an ANNA-B112 module and a custom built
application.
It is not mandatory to use this EEPROM solution; if not used, the two ANNA pins -
IO_42 and IO_41
can be without configurations.
Two pull-up resistors - R44 and R50, can be added to the I
2
C lines if needed. They are not mounted
on the evaluation board by default.
Visit
https://github.com/raspberrypi/hats/blob/master/designguide.md
for more information on the
ID EEPROM specification.
