NCN51205GEVB
http://onsemi.com
17
6.
What is the usage of ARXD and ATXD
(Figure 11)?
These pins have no meaning and cannot be used.
7.
I’ve tried all possible R6 and R9 combinations but
I’m not capable of setting V
DD2
above 6 V. How
does this come?
As can be seen in Figure 10, V
DD2
(5 V) is
connected to an ESD protection diode (D14). This
is a 5 V ESD protection diode. Whenever one tries
to set V
DD2
above 5 V, this ESD diode will trigger
and limit the V
DD2
voltage to about 6 V.
This issue can be solved by, or removing D14 (in
an ESD safe area this should not be an issue), or
by replacing this 5 V ESD diode with a higher
voltage version (see the SMFxxA datasheet for
other versions (www.onsemi.com)).
8.
Is it possible to test all interfaces (UART, SPI,
Analog Mode) with KNX REV5?
Yes, the KNX REV5 board can be used with all
possible interfaces. One has to be careful however
when using the Analog Mode. In the Analog Mode
the digital of NCN5120 is bypassed. If the
microcontroller would force the RXD
−
pin (pin 29)
of NCN5120 low, NCN5120 would pull the KNX
bus low which could lead to issues.
9.
Is it possible to bypass the microcontroller on the
KNX REV5 board and connect NCN5120 directly
with our microcontroller board?
Although the board is not designed for this, this is
possible. One could connect NCN5120 directly to
your microcontroller board by soldering some
wires on the KNX REV5 board. It is however
advised to remove the microcontroller from the
KNX REV5 board or to put the microcontroller in
reset (short pins 8 and 7 of J4 (see Figure 10)).
In case one wants to use the UART interface (9-bit
UART, 19 200 bps) or Analog Mode, one could
even use connector J2. The KNX_TXD and
KNX_RXD give a direct connection to the TXD-
and RXD-pin of NCN5120. Because the MODE1-,
MODE2- and TREQ-pin have an internal pull
down, one does not even need to connect these
pins for UART mode. For Analog Mode one can
use J6 to make the TREQ-pin high.
10.
I’m trying to sink more than 13 mA from the KNX
bus with KNX REV5 but I’m having issues with the
voltage regulators whenever I’m going above
16 mA. What could be the issue?
To be able to take more than 13 mA from the KNX
bus one needs to pull the FANIN/WAKE
−
pin of
NCN5120 low. This can be done by shorting J5
(add jumper).
See NCN5120 datasheet for more info on the
FANIN/WAKE
−
pin.
Table 6. INTERFACE SELECTION
TREQ
MODE2
MODE1
SCK/UC2
SCB/UC1
SDI/RXD
SDO/TXD
Description
0
0
0
0
0
RXD
TXD
9-bit UART-Mode, 19,200 bps
0
0
0
0
1
9-bit UART-Mode, 38,400 bps
0
0
0
1
0
8-bit UART-Mode, 19,200 bps
0
0
0
1
1
8-bit UART-Mode, 38,400 bps
1
0
0
X
X
Driver
Receiver
Analog Mode
TREQ
0
1
SCK (out)
CSB (out)
SDI
SDO
SPI Master, 125 kbps
TREQ
1
0
SPI Master, 500 kbps
NOTE: X = Don’t Care
