Digilent 6003-410-000P-KIT - Manual (Page 61)

XUP Virtex-II Pro Development System www.xilinx.com 61
UG069 (v1.0) March 8, 2005
Using the Serial Ports R
bit, and odd parity. The data packets are organized differently for mouse and keyboard
data. In addition, the keyboard interface supports bidirectional data transfer so the host
device can drive the status
LEDs on the keyboard.
The PS/2 port operates as a serial interface with a bidirectional data signal and a
unidirectional clock signal. Both of these signals operate as open-drain signals, defaulting
to a logical 1, at 5V through the use of a week pull-up resistor. To transmit a logical 0, the
signal line is actively pulled to ground. In the case of the data line, both the host and the
attached peripheral are able to drive the signal low. In the case of the clock signal, only the
host is able to drive the signal low, giving the host control of the speed of the interface.
Figure 2-18 shows the implementation of the PS/2 keyboard port used on the XUP Virtex-
II Pro Development System. The implementation of the PS/2 mouse port is identical
except for the signal names and the part reference designator.
The bidirectional level shifter shown in Figure 2-18 is used to interconnect two sections of
the PS/2 port, each section with a different power supply voltage and different logic levels.
The level shifter for each signal consists of one discrete N-channel enhancement MOS-FET.
The gate of the transistor must be connected to the lowest supply voltage (VCC3V3); the
source connects to the signal on the lower voltage side; and the drain connects to the signal
on the higher voltage side.
Figure 2-17: RS-232 Serial Port Implementation
RS232_DSR_OUT
RS232_TX_DATA
RS232_CTS_OUT
RS232_RX_DATA
RS232_RTS_IN
DSR
RXD
CTS
TXD
RTS
MAC3388ECUG
RS-232 DCE
J11
VCC2V5
C445 U28
C447 C446
C449
C448
0.1UF
0.1UF
0.1UF
0.1UF
0.1UF
SHDN
C1+
C2+
C1-
C1-
T1IN T1OUT
V-
V+
T2OUT
T3OUT
R1IN
R2IN
LIN
SWIN
T2IN
T3IN
R1OUT
R2OUT
LOUT
SWOUT
GND
VCC VL
2.5V RS-232
Transceiver
1
24 23 14
3
4
5
7
2
6
21
20
19
18
17
16
15
22
8
9
13
12
10
11
1
2
3
4
5
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8
9
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