Digilent DIO1 User Manual

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Revision: May 10, 2004 215 E Main Suite D | Pullman, WA 99163

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Overview

The Digital I/O board 1 (the DIO1) is one of
several expansion boards designed to mate with
Digilent system boards. The DIO1 is an
inexpensive board that contains an assortment
of basic digital I/O devices, including buttons,
switches, and several LED displays. The DIO1
board can be combined with Digilab system
boards to provide a source of ready-made I/O
devices, allowing a wide range of projects to be
implemented without the need for any other
components.

DIO1 board features include:

• A four digit seven-segment LED display;

• 8 individual LEDs;

• A 3-bit VGA port;

• 5 momentary pushbuttons;

• 8 slide switches;

• A PS2 mouse/keyboard port.

Functional description

The DIO1 board has been designed to provide a
basic, inexpensive platform that contains many
of the I/O devices commonly found in digital
systems. Unlike the more advanced DIO2
board, the DIO1 board has been designed so
that all signals pass directly to an attached
system board, so no intermediate logic is
required. When mated with a Digilab system
board, the DIO1 board can provide a flexible
prototyping system that can be operational
immediately.

LEDs

Eight LEDs are provided for circuit outputs.
The LED cathodes are tied to ground via 270­ohm resistors, and the anodes are driven from
the 74HC373 (so the LED drive signals are
active high).

®

Connector B

5

12

5 buttons

LD signals

9

8

74HC373

Latch

8 LEDs

Figure 2. LED Circuit

LD1- LD8

RP1
270 Ohm

GND

VGA Port

Connector A

5

2

PS2
port

4 displays 8 switches

Figure 1. DIO1 schematic

Signals

All named signals used on the DIO1 board are
defined in the Table 1. Voltage levels for all

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signals arriving from an attached Digilab
system board are determined by the system
board, but all signals arising on the I/O board
derive from the on-board 5VDC regulator (so
they are all 5V CMOS signals).

The DIO1 board uses a two-layer process, so
all signals are available on the top and bottom
layers. Many signals are brought to a test point
header for easy test and measurement
equipment attachment.

Power Supply

The DIO1 board receives system power from
pins 39 and 37 of connectors A and B (which
mate to pins 1 and 3 of an attached system
boards). Pin 37 provides Vdd from the attached
system board (assumed to be 3.3VDC), and pin
39 is connected to ground. Up to 5VDC can be
safely applied to the Vdd input pin (pin 37).
The DIO1 board typically consumes less than
10mA with no LED’s illuminated, and up to
130mA with all LEDs illuminated (including

Power Supplies
VU Unregulated power supply voltage from

attached system board – typically 5­9VDC. Although connected to the board,
this supply is not used on the DIO1
board.

VDD33 Regulated power supply voltage

(3.3VDC) from attached system board.
All devices on DIO1 board use this

supply.
GND System ground
VGA signals
HS VGA Horizontal Sync signal
VS VGA Vertical Sync signal
R VGA 1-bit red data
G VGA 1-bit green data
B VGA 1-bit blue data
PS2 signals
KCLK PS2 (Keyboard or Mouse) clock signal
KDAT PS2 (Keyboard or Mouse) data signal
Input devices
BTN1-4 Pushbuttons 1 through 4
SW1-

SW8
Output devices
LD0-LD8 Discreet LEDs 1 through 8
CA-CF Seven-segment display cathodes
AN1-

AN3

Table 1. DIO1 board signal definitions

Slide switches 1 through 8

Seven-segment display anodes

all segments of the seven-segment display).

Seven-segment LED display

The DIO1 board contains a modular 4-digit,
common anode, seven-segment LED display.
In a common anode display, the seven anodes
of the LEDs forming each digit are connected
to four common circuit nodes (labeled AN1
through AN4 on the DIO1 board). Each anode,
and therefore each digit, can be independently
turned on and off by driving these signals to a
‘1’ or a ‘0’. The cathodes of similar segments
on all four displays are also connected together
into seven common circuit nodes labeled CA
through CG. Thus, each cathode for all four
displays can be turned on and off
independently.

This connection scheme creates a multiplexed
display, where driving the anode signals and
corresponding cathode patterns of each digit in
a repeating, continuous succession can create a
4-digit display. In order for each of the four
digits to appear bright and continuously
illuminated, all four digits should be driven
once every 1 to 16ms (for a refresh frequency
of 60Hz to 1KHz). For example, in a 60Hz
refresh scheme, each digit would be illuminated
for ¼ of the refresh cycle, or 4ms. The
controller must assure that the correct cathode
pattern is present when the corresponding
anode signal is driven. To illustrate the process,
if AN1 is driven high while CB and CC are
driven low, then a “1” will be displayed in digit
position 2. Then, if AN2 is driven high while
CA, CB and CC are driven low, then a “7” will
be displayed in digit position 2. If AN1/CB, CC
are driven for 4ms, and then AN2/CA, CB, CC

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are driven for 4ms in an endless succession, the

Refresh period = 1ms to 16ms

display will show “17” in the first two digits.
An example timing diagram is provided to the
right.

Anodes

via transistors for greater current

-- connected to CPLD

Vdd

a2

a3a4

a1

AN1
AN2
AN3
AN4

Digit period = Refresh / 4

Cathodes

Seven segment display refresh signals and timings

Digit 1 Digit 2 Digit 3 Digit 4

abcdefgdp

Cathodes

CPLD pins via 100

-- connected to

Ω

resistor

a

f

.

e

b

g

c

Common anode

d

(a) (b)

afgedcb

Figure 3. (a) Seven segm e nt display deta il.
(b) comm on a node display configuration. (c)
segement illumination patterns for decimal
digits. (d) segm e nt illum ination truth table.

VCC

4.7KOhm

To Connector

GND

.01uF

GND

Digit

Show

n

(c)

0
1
2
3
4
5
6
7
8
9

Illuminated Segment

a b c d e f g

1 1 1 1 1 1 0
0 1 1 0 0 0 0
1 1 0 1 1 0 1
1 1 1 1 0 0 1
0 1 1 0 0 1 1
1 0 1 1 0 1 1
1 0 1 1 1 1 1
1 1 1 0 0 0 0
1 1 1 1 1 1 1
1 1 1 1 0 1 1

(d)

Push Buttons

The 5 momentary-contact push buttons are
normally high when unused; this high signal is
translated to a low signal by a Schmitt Trigger.
When the button is actively pressed the signal
is driven low, which the Schmitt Trigger will
translate to a high signal. The buttons exhibit a
worst-case bounce time of about 1ms. A
74HC14 Hex Schmitt Trigger inverter provides
the debounce filtering and ESD protection. The
button outputs are brought out directly to pins
on interface connector B.

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