Digilent Digilab 2 - Manual (Page 5)

Digilent Digilab 2 Reference Manual Digilent, Inc.
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source of data, and the DCE the peripheral device. Two DTE devices can be connected via a serial
cable, only if lines two and three are crossed – this is referred to as a null modem cable. A DTE and
DCE device can be connected with a straight-through cable. The Digilab 2 board is configured as a
DCE device.
DB9 top-down
hole pattern; cable
attaches from this side
Pin 1
Pin 6 Pin 9
Pin 5
DB9 serial port connector
Front view
Pin 1 Pin 9
1
6
2
7
3
8
4
9
5
GND
Maxim
MAX3386E
RS232 Voltage
Converter
RXD
TXD
16
DB9
Connector
RTS
CTS
Serial Port Pin Definitions
Pin # Name Function Direction Connected
1 DCD Data carrier detect DCE DTE N
2 RXD Received data DCE DTE Y
3 TXD Transmitted data DCE DTE Y
4 DTR Data terminal ready DCE DTE N
5 SG Signal ground Y
6 DSR Data set ready DCE DTE Y
7 RTS Request to send DCE DTE Y
8 CTS Clear to send DCE DTE Y
9 RI Ring Indicator DCE DTE N
Xilinx
Spartan 2
PQ208
DSR
17
13
14
15
8
7
10
11
9
P200
P202
P195
P201
P199
Figure 3. Serial port circuit schematic
Oscillator
The Digilab 2 uses a socketed half-size 8-pin DIP oscillator. The board ships with a 50MHz oscillator,
allowing for system clocks ranging from DC to 200MHz (using the Spartan 2 DLL circuit and/or clock
counter-dividers). Oscillators from 32KHz to 100MHz can easily be substituted, allowing for a wide
range of clock frequencies. The oscillator, which is connected to the FPGA GCK0 input (P80), is
bypassed with a 0.1uF capacitor and it is physically located as close to the FPGA as possible (trace
length is about 10mm).
Power Supplies
The Digilab 2 board uses two LM317 1.5A voltage regulators to produce 2.5VDC and 3.3VDC
supplies. The regulator inputs are driven from an external DC power supply connected to the on-board
2.1mm center-positive power jack. The regulators have 10uF of input capacitance, 20uF of local output
capacitance, and 10uF of regulation bypass capacitance. This allows the regulators to produce stable,