Which Pins Connect to the E5’s Dedicated UART?

Unlike the original 8051, the E5’s embedded 8051 does not use any dedicated I/O pins. Nearly everything is programmable, including the pins that connect to the E5’s dedicated UART.

The following example demonstrates how to connect the E5’s dedicated UART directly to pins. The example assumes that you are using UART modes 1, 2, or 3. Mode 0 requires a slightly different configuration.

To connect the UART’s transmit signal, TXD, type output in the soft IP module library selector. Double-click Output v.2.

Choose "Output" from the FastChip soft Ip module library.

Type TXD for the Component Name. Connect the output to the UART’s TXD signal, either by typing TXD in connection textbox or by clicking the connection browser button ().

Type "TXD" for the Component Name. Connect the output to the sideband signal called "TXD".

FastChip’s connection browser allows you to pick various signals that exist in your design. Even in a new project, there are some pre-existing, dedicated signals to and from the dedicated resources. Triscend calls these signals sideband connections. The UART transmit signal TXD is an example.

Click MCU to expand the tree. Then click TXD to expand the transmit sideband signal. Click on TXD to select the TXD signal. Finally, click OK to make the connection. Click OK to close the Output module dialog box.

Using FastChip's connection browser, you can connect to the TXD signal by expanding "MCU", then "TXD", then selecting "TXD". Click "OK" when finished.

Now connect the UART’s receive input. Type input in the soft IP module library selector. You may need to click the >> button to find the next occurrence of the word “input” in the library. When found, double-click Input v.2.

To connect the UART receive input, find the Input module in the FastChip soft IP module.

Type RXD for the component name. Either type the signal name RXD_In or use FastChip’s connection browser and find RXD_In, which connects to the MCU. When finished, click OK to close the Input module dialog box.

Enter "RXD" for the Component Name and "RXD_In" for the connection name.

The UART also has a RXD_Out sideband signal that is only used in Mode 0.

Because the UART connections are sideband signals, you can connect them to any available PIO pin on the device. To place the I/O pins, select Constraints à I/O Editor from FastChip’s menu or click the I/O Editor button in the toolbar.

Click the Bind button in the FastChip toolbar.

To place the TXD output pin, expand the TXD folder, then expand the Output Signals folder, then click and hold the mouse button on TXD. Drag the pin to an available I/O and then release the mouse button to place the TXD pin on the selected PIO pin. Do the same for the RXD input pin.

Expand "TXD" and "Output Signals". Click and hold the mouse button on the TXD output. Drag the output to the desired PIO pin and then release the mouse button.

Again, you can choose any available PIO pin for the UART’s transmit and receive signals. Click OK when finished. Now Bind your project to create the physical connections between the embedded 8051’s UART and the specified PIO pins.

Example of how TXD and RXD signals can be placed on any available PIO pin.

RS232 connections on the E5 Development Platform board.

On the E5 Development Platform board, there are two 9-pin RS232 connectors. You can connect the E5’s UART to either RS232 driver. The following table shows the TE520 pins that connect to the RS232 ports.

RS232 Port	TXD Pin	RXD Pin
RS232-1	117	63
RS232-2	79	84

FastChip Version: 2.4.0

This solution may or may not apply to other versions of the FastChip development system.