NCN5121_16 Datasheet, PDF (26/58 Pages) ON Semiconductor – Transceiver for KNX Twisted Pair Networks

NCN5121
Interface Mode
The device can communicate with the host controller by
means of a UART interface or an SPI interface. The
selection of the interface is done by the pins MODE1,
MODE2, TREQ, SCK/UC2 and CSB/UC1.
Table 9. INTERFACE SELECTION
TREQ
MODE2
MODE1
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
TREQ
0
1
TREQ
1
0
NOTE: X = Don‘t Care
SCK/UC2
0
0
1
1
DC2EN
SCK (out)
CSB/UC1
0
1
0
1
V20VEN
CSB (out)
SDI/RXD
RXD
Driver
SDI
SDO/TXD
TXD
Receiver
SDO
Description
9−bit UART−Mode, 19200 bps
9−bit UART−Mode, 38400 bps
8−bit UART−Mode, 19200 bps
8−bit UART−Mode, 38400 bps
Analog Mode
SPI Master, 125 kbps
SPI Master, 500 kbps
UART Interface
The UART interface is selected by pulling pins TREQ,
MODE1 and MODE2 to ground. Pin UC2 is used to select
the UART Mode (‘0’ = 9−bit, ‘1’ = 8−bit) and pin UC1 is
used to select the baudrate (‘0’ = 19200 bps, ‘1’ =
38400 bps). The UART interface allows full duplex,
asynchronous communication.
The difference between 8−bit mode and 9−bit mode is that
in 9−bit an additional parity bit is transmitted. This parity bit
is used as an even parity bit (with exception of the internal
register read and write services where the parity bit is
meaningless and should be ignored). However, when the
NCN5121 detects an acceptance window error or pulse
duration error on the KNX bus, the parity bit is also encoded
to indicate an error in the byte. In 8−bit mode one extra
service is available (U_FrameState.ind). The SDI/RXD−pin
is the NCN5121 UART receive pin and is used to send data
from the host controller to the device. Pin SDO/TXD is the
NCN5121 UART transmit pin and is used to transmit data
between the device and the host controller. Figure 12 gives
an UART application example (9−bit, 19200 bps). Data is
transmitted LSB first.
Start
(= 0)
Bit 0
Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
Figure 22. 8−bit UART Mode
Bit 6
Bit 7
Stop
(= 1)
Start
(= 0)
Bit 0
Bit 1
Bit 2 Bit 3 Bit 4 Bit 5 Bit 6
Figure 23. 9−bit UART Mode
Bit 7
Parity
Stop
(= 1)
One special UART Mode is foreseen called Analog Mode.
When this mode is selected (TREQ = ‘1’, MODEx = ‘0’) an
immediate connection is made with the KNX transmitter
receiver (see Figure 24). Bit level coding/decoding has to be
done by the host controller. Keep in mind that the signals on
the SDI/RXD− and SDO/TXD−pin are inverted. Figure 14
gives an Analog Mode application example. In Analog
Mode, the UC1 and UC2 pins are used to enable or disable
the 20 V regulator and DC2 controller. When pulled low,
these blocks are enabled. When one of these pins is pulled
to VDDD, the respective block is disabled. When using the
device in Analog Mode, no clock needs to be provided to the
device.
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