EVK-NORA-B1 - User guide
UBX-20030319 - R05
Hardware description
Page 11 of 32
C1-Public
Figure 6: UART level shifters and disable switches
☞
Figure 6 reflects Rev D and Rev E hardware versions.
☞
For Rev C or earlier hardware versions, applications need to map the following
VCOM0
handshake
signals:
o
VCOM0_RTS
= P0.12
o
VCOM0_CTS
= P0.10
o
VCOM0_TxD
= P1.00 (no change)
o
VCOM0_RxD
= P1.01 (no change)
2.6
32.768 kHz low frequency clock
The low frequency (LF) clock of the NORA-B1 module can have one of four sources:
•
Internal ultra-low power RC oscillator – for low-precision timing where low power is the main
requirement
•
Internal calibrated RC oscillator – for applications with no strict real-time requirements
•
Internal synthesized clock – derived from the 32 MHz clock
•
External crystal oscillator – offers the most accurate and lowest power LF clock
The evaluation board has a 32.768 kHz crystal connected to the NORA-B1 module to allow use of the
external crystal oscillator option. Loading capacitors for the oscillator circuit are internal to the nRF53
within the module. Values of 6 pF, 7 pF, and 11 pF can be enabled through register XOSC32KI.INTCAP.
If an internal LF clock source is used, the crystal can be removed from the circuit by opening jumpers
J16 and J19. Soldering across the normally open position connects XL1 and XL2 to the EVK headers.
