NB2DSK01 - RS-232 Serial Port

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Modified by Admin on Sep 13, 2017

The NB2DSK01 provides a PC-style RS-232 serial interface. A DB-9 Male connector is used to provide a serial port, wired as a DCE (Data Communication Equipment), in accordance with the EIA-574 standard. Connection to a host PC (wired as a DTE (Data Terminal Equipment)) can be achieved using a null modem serial cable.

Figure 1. RS-232 serial interface port.

Signal level translation – CMOS to RS-232 and vice-versa – is provided using a MAX3232EUE RS-232 Transceiver device (from Maxim). This device has 2 receivers and 2 drivers, the use of which is summarized as follows:

Receivers – used for the RXD (pin 2) and CTS (pin 8) signals, received from the host PC over the RS-232 interface and subsequently wired to pins of the daughter board FPGA.

Drivers – used for the TXD (pin 3) and RTS (pin 7) signals, sourced from the design running in the daughter board FPGA device for transmission to the PC over the RS-232 interface.

The MAX3232 is compatible, both in terms of pinout and functionality, with the industry standard MAX232 device.

The MAX3232 is powered from the NB2DSK01's 3.3V supply and incorporates a dual charge pump, requiring four 0.1uF external charge pump capacitors. RS-232 output levels are maintained at a guaranteed data rate of 120kbps.

The incoming Data Terminal Ready signal (DTR) – which arrives on pin 4 of the connector – is wired, on the motherboard, directly to the outgoing pins for the Data Set Ready (DSR) and Data Carrier Detect (DCD) signals (pins 6 and 1 respectively). The Ring Indicator signal (RI) arriving on pin 9 of the connector, is not used.

Location on Board

The MAX3232 device (designated U13) and associated external capacitors are located on the solder side of the board.

Figure 2. MAX3232 device and
related circuitry.

The DB9M (Male) connector (designated J9) is located on the component side of the board, to the immediate left of the CAN interface port.

Schematic Reference

The RS-232 interface circuitry can be found on the following sheets of the motherboard schematics:

Sheet 50 (RS232_MAX3232.SchDoc, entitled RS232COMMS_1)

Sheet 51 (CON_RS232DCE_DB9.SchDoc, entitled RS232-DCE DB9).

Design Interface Component

Table 1 summarizes the available design interface component that can be placed from the FPGA NB2DSK01 Port-Plugin.IntLib, to access and use the RS-232 interface.

Table 1. RS-232 port-plugin component.

Component Symbol	Component Name	Description
	`RS232CNTR`	Place this component to interface to the MAX3232 device and subsequent RS-232 serial port.

Further Device Information

For more information on the MAX3232 device, refer to the associated datasheet (MAX3222-MAX3241.pdf) available at www.maxim-ic.com.