Digilent DIO5 User Manual

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Overview

The DIO5 circuit board provides a ready-made

Connector P2Connector P1

source for many common I/O devices found in digital systems. It can be connected to Digilent system boards to create a digital development platform that is suitable for a wide range of projects. The DIO5 uses a Xilinx CoolRunner CPLD to facilitate interaction with system boards. The CLPD automatically appears in the JTAG scan chain when the DIO5 is

JTAG

XCR3128XL CoolRunner CPLD

Clock

System Bus

TQ-144

VGA

Port

Uncomitted I/O

attached to a system board, so new designs can easily be configured into the DIO5. DIO5 features include:

• A Xilinx CoolRunner XCR3128 CPLD for I/O device and system bus control;

• A 16x2 character LCD module;

• A 4-digit seven segment LED display;

• 16 LEDs in three different colors;

8 switches

16x2 LCD

DIO5 circuit board block diagram

PS2 Port

4 7-seg.

displays

16 LEDs

16 button

keypad

• A 16 button keypad;

• 8 slide switches;

• 3-bit VGA port;

• PS/2 mouse or keyboard port.

The DIO5 has been designed to work seamlessly with Digilent system boards and all versions of the Xilinx ISE CAD tools, including the free WebPack tools available from Xilinx. The CPLD on the DIO5 is configured during manufacturing with the project shown in Appendix 1, but new designs can easily be loaded into the CPLD.

Functional Description

The Digilab DIO5 can be attached to any Digilent system board to create a digital design platform that has many useful I/O devices. The DIO5 draws power from the system board, so no separate power supply is required. All I/O device signals are routed through the on-board CPLD so that a customized I/O controller can be created for any given design. For example,

if all on-board I/O devices are needed, a register-based controller can be implemented. Or, if only a subset of I/O devices are needed, a much simpler controller can be used to map device signals directly through the CPLD to the system board. Because the CPLD appears in the JTAG scan chain when the DIO5 is attached to a system board, it can easily be configured. The CPLD is programmed during manufacture with register-based controller shown in Appendix 1.

Power Supplies

The DIO5 board draws power from three pins on the 40-pin connectors: pin 37 supplies 3.3V; pin 39 provides system GND, and pin 40 supplies unregulated voltage (VU). Pin 40 (VU) is connected directly to an LM1117 5VDC LDO regulator on the DIO5. 5VDC is used by the LCD display and the PS/2 interface. The 3.3V

DIO5 Reference Manual Digilent, Inc.

supply is used to drive the CPLD and all other I/O devices on the board. During normal operation, the DIO5 consumes 10-20mA from the 5V supply, and 50-100mA from the 3.3V supply depending on how many LEDs are illuminated. The DIO5 uses a four-layer board, with two layers dedicated to 3.3V and GND, and several bulk and high-frequency decoupling capacitors to keep the supplies stable under all loads.

CPLD Configuration

The JTAG scan chain is routed through the DIO5 board on pins 1-4 of connector P1, allowing the CPLD to be configured from any Digilent system board. Jumper-shunts must be loaded on pins 1 & 2 of jumper blocks JP2 and JP3 on the DIO5 to include the CPLD in the scan chain, or across pins 2 & 3 to remove the CPLD from the scan chain.

Jumper position JP1 allows the JTAG signals on the CPLD to be reclaimed if they are inadvertently programmed as user I/O’s. Since the JTAG pins on the CPLD are used only for programming, this jumper block should not normally be loaded. The CPLD pinout is available in appendix 1.

System Board Interface

Signals from all I/O devices on the DIO5 are routed through the CPLD, with the exception of the VGA port (video data is too high bandwidth to pass through the CPLD). All I/O devices on the DIO5 can therefore be read or written via a register-based controller in the CPLD. Some device signals, including the eight slide switches, the PS/2 data and clock, and an LCD enable are also routed around the CPLD and directly to the connectors. These signals can be accessed either through the CPLD or directly from the system board.

The CPLD offers several options for moving data between the DIO5 and a system board: a memory-mapped bus interface can be defined where all devices are accessed via registers; a “direct connect” interface can be defined where

I/O signals pass directly through the CPLD without the need for a bus (in this case, not all devices on the DIO5 can be accessed); or various controllers and compression/encoding schemes can be used to transfer device data over subsets of pins.

The default DIO5 CPLD circuit defines a “system bus” to transfer data to and from a system board. The bus uses 8 bi-directional data lines, six address lines, three control signals, and a clock signal (LCLK). The three control signals, write enable (WE), output enable (OE), and chip select (CS), are used to coordinate bus traffic, and the LCLK signal provides a clock for latches and controllers on the DIO5. Four 8-bit write-only registers are used to receive LED and seven-segment display data in the CPLD, and three readable locations contain pushbutton and switch data.

DIO5 Default Circuit Memory Map

Address Read Write

000 BtnLo (buttons 0-7) LedLo (LEDs 0-7) 001 BtnHi (buttons 8-F) LedHi (LEDs 8-F) 010 Swt (slide switches) SsegLo 011 unused SsegHi

10X LCD bus LCD bus

Two read locations, BtnHi and BtnLo, arise from latches in the CPLD. Pushbutton signals are stored in these two 8-bit latches at each rising edge of LCLK. The third read location, Swt, simply passes switch signals to the system bus from the switch input pins.

The four writable registers in the CPLD all provide data to the LED devices (i.e., the seven-segment displays and discrete LEDs). The registers use rising-edge-triggered flipflops clocked by the trailing edge of the write enable signal (WE is active low). Data written to these registers appears immediately on the LED’s.

Ten additional pushbutton signals bypass the system bus, and are routed from the CPLD directly to pins on the expansion connectors. Four of these signals contain BCD codes for buttons 0-9, and six signals are simply the state of buttons A-F at the output of the

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DIO5 Reference Manual Digilent, Inc.

latches. These ten signals are always available regardless of the system bus state.

The CPLD also contains a seven-segment display controller. Binary data, in the form of four 4-bit fields spanning two bytes, can be written to the seven-segment data registers and it will be displayed as four hexadecimal characters on the seven-segment display. The display controller uses LCLK to control refresh timing.

Bi-directional LCD data transfers occur over the system bus. The default CPLD circuit synthesizes LCD control signals for bus cycles directed to the LCD memory space, but it is also possible to drive the LCD control signals directly. The “LCD” section below provides information on driving the LCD.

Write Cycle

tdoe

DB0-DB7

Read Cycle

DB0-DB7

System Bus Timing

ten

twd

System bus timings are shown below. Data is written on the rising edge of write-enable (WE). DIO5 bus drivers are enabled whenever output enable (OE) is asserted (low). The diagrams below show signal timings assumed by Digilent to create peripheral devices. Different bus and timing models can be used by modifying circuits in the FPGA and attached peripheral devices.

System Bus Timings

Symbol Parameter

ten Time to enable after CS asserted 10ns

th Hold time 1ns tdoe Disable time after OE deasserted 10ns teoe Enable time after OE asserted 15ns

tw Write strobe time 10ns

tsu Data setup time 5ns

twd Write disable time 0ns

teoe

tsu

teoe

tdoe

tsu

Read data latch time

Time

(typ)

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DIO5 Reference Manual Digilent, Inc.

LCD

The DIO5 uses a Powertip 16x2 LCD module (P/N PC1602ARS-DWA-A) with a Samsung KS0066U controller (data sheets are available at the Digilent website).

16 x 2 character LCD

Pin 1

Powertip PC1602ARS

The KS0066U contains a character-generator ROM (CGROM) with 208 preset 5x8 character patterns, a character-generator RAM (CGRAM) that can hold 8 user-defined 5x8 characters, and a display data RAM (DDRAM) that can hold 80 character codes. Character codes written into the DDRAM serve as indexes into the CGROM (or CGRAM). Writing a character code into a particular DDRAM location will cause the associated character to appear at the corresponding display location. Display positions can be shifted left or right by setting a bit in the instruction register (IR). The write-only IR directs display operations (such as clear display, shift left or right, set DDRAM address, etc). Available instructions (and the associated IR codes) are shown in the rightmost column of table 3 below. A busy flag shows whether the display has competed the last requested operation; prior to initiating a new operation, the flag can be checked to see if the previous operation has been completed.

The display has more DDRAM locations than can be displayed at any given time. DDRAM locations 00H to 27H map to the first display row, and locations 40H to 67H map to the second row. Normally, DDRAM location 00H maps to the upper left display corner, and 40H to the lower left. Shifting the display left or right can change this mapping. The display uses a temporary data register (DR) to hold data during DDRAM /CGRAM reads or writes, and an internal address register to select the RAM location. Address register contents, set via the

IR, are automatically incremented after each read or write operation. The LCD display uses ASCII character codes. Codes up through 7F are standard ASCII (which includes all “normal” alphanumeric characters). Codes above 7F produce various international characters – please see the manufacturers data sheet for more information on international codes.

The display is connected to the DIO5 board by a 16-pin connector (pins 15 and 16 are for an optional backlight, and they are not used). The 14-pin interface includes eight data signals, three control signals, and three voltage supply signals. The eight data bus signals are passed through the CPLD to/from the system bus for read/write cycles directed to the LCD memory space (address 10X). The three LCD control signals are driven from the CPLD: the RS (Register Strobe) signal clocks data into registers; the R/W signal determines bus direction; and the E signal enables the bus for read or write operations. In the standard CPLD configuration, the R/S and R/W signals are connected to ADDR0 and WE respectively. The E signal can be driven directly from the LCDEN signal available on the system connector, or if LCDEN is left at logic ‘0’, then E is driven whenever address “10X” is present on the bus, CS is asserted, and AS or DS are low. LCD bus signals and timings are shown below.

A startup sequence with specific timings ensures proper LCD operation. After power-on, at least 20ms must elapse before the functionset instruction code can be written to set the bus width, number of lines, and character patterns (8-bit interface, 2 lines, and 5x8 dots are appropriate). After the function-set instruction, at least 37us must elapse before the display-control instruction can be written (to turn the display on, turn the cursor on or off, and set the cursor to blink or no blink). After another 37us, the display-clear instruction can be issued. After another 1.52ms, the entrymode instruction can set address increment (or address decrement) mode, and display shift mode (on or off). After this sequence, data can be written into the DDRAM to cause information to appear on the display.

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DIO5 Reference Manual Digilent, Inc.

Table 3. LCD Instructions and Codes

Instruction

Clear

Display

Return

Home

Entry mode

set

Display

ON/OFF

control

Cursor or

Display shift

Function Set 0 0 0 0 1 DL N F X X

Set CGRAM

Address

Set DDRAM

address

Read busy

flag/ address Write data to

RAM

Read data

from RAM

RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0

0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 1 X

0 0 0 0 0 0 0 1 I/D SH

0 0 0 0 0 0 1 D C B

0 0 0 0 0 1 S/C R/L X X

0 0 0 1 AC5 AC4 AC3 AC2 AC1 AC0 Set CGRAM address counter 0 0 1 AC6 AC5 AC4 AC3 AC2 AC1 AC0 Set DDRAM address counter 0 1 BF AC6 AC5 AC4 AC3 AC2 AC1 AC0

1 0 D7 D6 D5 D4 D3 D2 D1 D0

1 1 D7 D6 D5 D4 D3 D2 D1 D0

Instruction bit assignments

Description

Clear display by writing a 20H to all DDRAM locations; set DDRAM address register to 00H; and return cursor to home. Return cursor to home (upper left corner), and set DDRAM address to 0H. DDRAM contents not changed. I/D = ‘1’ for right-moving cursor and address increment; SH = ‘1’ for display shift (direction set by I/D bit). Set display (D), cursor (C), and blinking cursor (B) on or off.

SC = ‘0’ to shift cursor right or left, ‘1’ to shift entire display right or left (R/L = ‘1’ for right). Set interface data length (DL = ‘1’ for 8 bit), number of display lines (N = ‘1’ for 2 lines), display font (F = ‘0’ for 5x 8 dots)

Read busy flag and address counter Write data into DDRAM or CGRAM, depending on which address was last set Read data from DDRAM or CGRAM, depending on which address was last set

Table 4. LCD Connector Signals

Pin No. Symbol Signal Description

1 Vss Signal ground 2 Vdd Power supply (5V) 3 Vo Operating (contrast) voltage (LCD drive, typically 100mV at 20C) 4 RS Register select: high for data transfer, low for instruction register 5 R/W Read/write signal: high for read mode, low for write mode 6 E Read/write strobe: high for read OE; falling edge writes data 7-14 Data Bus Bi-directional data bus

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DIO5 Reference Manual Digilent, Inc.

LCD Read Cycle

R/W

tsu

tr tf

tD tDH

Power On

Wait for 20ms

Function Set

Wait for 37us

Display Control Set

DB0-DB7

Wait for 37us

Display Clear

Wait for 1.52ms

OK for operati o ns

LCD startup sequence

LCD Write Cycle

R/W

tsu

tsu1 th1

DB0-DB7

Enable cycle time tc 500 ns E Enable High pulse width tw 220 ns E Enable rise/fall time tr, tf 25 ns E RS, R/W setup time tsu 40 ns RS, R/W RS, R/W hold time th 10 ns RS, R/W Read data output delay tD 60 120 ns DB0-DB7 Read data hold time tDH 20 ns DB0-DB7 Write data setup time tsu1 40 ns DB0-DB7 Write data hold time th1 10 ns DB0-DB7

Parameter Symbol Min Max Unit Test Pin

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Table 5. LCD Bus Timings

DIO5 Reference Manual Digilent, Inc.

Seven-Segment LED display

The DIO5 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 A1 through A4 on the DIO5). 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 1KHz to 60Hz). 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 A1 is driven high while CB and CC are driven low, then a “1” will be displayed in digit position 2. Then, if A2 is driven high while CA, CB and CC are driven low, then a “7” will be displayed in digit position 2. If A1 and CB, CC are driven for 4ms, and then A2 and CA, CB, CC are driven for 4ms in an endless succession, the display will show “17” in the first two digits. An example timing diagram is provided below.

Common anode

A2 A3

Refresh period = 1ms to 16ms

afgedcb

Digit period = Refresh / 4

f e

Seven-segment display detail and cathaode patterns to display the decimal digits.

Anodes are connected via

transistors for greater current

Vdd

Digit Shown

0 1 2 3 4 5 6 7 8 9

A2A1

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

Cathodes Digit 1 Digit 2 Digit 3 Digit 4

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Cathodes are connected to

Xilinx device via 100Ω resistors

cdef gdp

DIO5 Reference Manual Digilent, Inc.

When configured with the code shown in the appendix, the CPLD on the DIO5 board implements a seven-segment controller provided a suitable clock (256Hz to 1KHz) is provided on the LCLK pin. The controller accepts four 4-bit binary numbers in two successive registers, and decodes and displays them.

Discrete LEDs

Sixteen individual LEDs (5

Vdd

green, 5 yellow, and 6 red) are provided for circuit outputs. The LED cathodes are driven directly from the

390

CPLD, and the anodes are tied to Vdd via 390-ohm resistors (so the LED drive signals are active low). When the CPLD is

LD# signal

configured with the code shown in the appendix, two 8-bit registers (at writable locations 000 and 001 in the CPLD) drive the LED cathode signals. Note the LED signals are inverted in the VHDL code, so a logic “1” turns on the LEDs.

Pushbutton Inputs

Outputs from the 16 momentary-contact push buttons are normally low, and are driven high only while the button is actively pressed. The buttons exhibit a worst-case bounce time of about 1ms. A 4.7K series resistor provides some debounce filtering and ESD protection to each button. When configured with the code shown in the appendix, the CPLD on the DIO5 board makes all button signals available on the bus in two successive readable address locations (0 and 1).

Vdd

BTN# signal

4.7KΩ

GND

Switch Inputs

The eight slide switches on the DIO5 can be used to connect either Vdd or GND to eight pins on the CPLD. The switches exhibit about 2ms of bounce, and no active debouncing circuit is employed. A 4.7K-ohm series resistor is used for nominal input protection. When configured with the code shown in the appendix, the CPLD makes all switch signals available on the system bus at address location 2.

Vdd

SW#

4.7KΩ

GND

signal

PS2 Port

The DIO5 board includes a 6-pin mini-DIN connector that can accommodate a PS2 mouse or PS2 keyboard connection. A 5VDC regulator provides the required voltage to keyboards and/or mice. Both the mouse and keyboard use a two-wire serial bus (including clock and data) to communicate with a host device. These signals are routed through the CPLD to provide voltage mapping, and to allow a controller to be placed in the CPLD.

Pin Definitions

Pin Function 1 Data 2 Reserved 3 GND 4 Vdd 5 Clock 6 Reserved

PS2 Connector

Pin 1

Pin 2

Pin 5Pin 6

Bottom-up

hole pattern

The keyboard and mouse both use identical signal timings. Both use 11-bit words that include a start, stop and odd parity bit, but the data packets are organized differently, and the keyboard interface allows bi-directional data transfers (so the host device can illuminate state LEDs on the keyboard). Bus timings are shown below. The clock and data signals are only driven when data transfers occur, and otherwise they are held in the “idle” state at logic ‘1’. The timings define signal requirements for mouse-to-

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DIO5 Reference Manual Digilent, Inc.

host communications and bi-directional keyboard communications.

Edge 0

CLK

DATA

HLD

'1' stop bit'0' start bit

Edge 10

Symbol Parameter Min Max

Clock time

Data-to-clock setup time

Clock-to-data hold time 5us 25us

HLD

30us

5us

50us 25us

Keyboard

The keyboard uses open collector drivers so that either the keyboard or an attached host device can drive the two-wire bus (if the host device will not send data to the keyboard, then the host can use simple input-only ports).

PS2-style keyboards use scan codes to communicate key press data (nearly all keyboards in use today are PS2 style). Each key has a single, unique scan code that is sent whenever the corresponding key is pressed. If

the key is pressed and held, the scan code will be sent repeatedly once every 100ms or so. When a key is released, a “F0” key-up code is sent, followed by the scan code of the released key. If a key can be “shifted” to produce a new character (like a capital letter), then a shift character is sent in addition to the original scan code, and the host device must determine which character to use. Some keys, called extended keys, send an “E0” ahead of the scan code (and they may send more than one scan code). When an extended key is released, an “E0 F0” key-up code is sent, followed by the scan code. Scan codes for most keys are shown in the figure below.

A host device can also send data to the keyboard. Below is a short list of some oftenused commands.

ED Set Num Lock, Caps Lock, and Scroll Lock

LEDs. After receiving an “ED”, the keyboard returns an “FA”; then the host sends a byte to set LED status: Bit 0 sets Scroll Lock; bit 1 sets Num Lock; and Bit 2 sets Caps lock. Bits 3 to 7 are ignored.

EE Echo. Upon receiving an echo command, the

keyboard replies with “EE”.

F3 Set scan code repeat rate. The keyboard

acknowledges receipt of an “F3” by returning an “FA”, after which the host sends a second byte to set the repeat rate.

FE Resend. Upon receiving FE, the keyboard re-

sends the last scan code sent.

FF Reset. Resets the keyboard.

ESC

` ~ 0E

TAB

Caps Lock

Shift

Ctrl

F105F206F304F4

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6 ^367 &3D8 *3E9 (460 )45- _4E= +55BackSpace

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Space

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[ {

; :

Alt

E0 11

' "

] }

\ |

Enter

Shift

Ctrl

E0 14

E0 75

E0 74

E0 6B

E0 72

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DIO5 Reference Manual Digilent, Inc.

The keyboard should send data to the host only when both the data and clock lines are high (or idle). Since the host is the “bus master”, the keyboard should check to see whether the host is sending data before driving the bus. To facilitate this, the clock line can be used as a “clear to send” signal. If the host pulls the clock line low, the keyboard must not send any data until the clock is released (hostto-keyboard data transmission will not be dealt with further here).

The keyboard sends data to the host in 11-bit words that contain a ‘0’ start bit, followed by 8bits of scan code (LSB first), followed by an odd parity bit and terminated with a ‘1’ stop bit. The keyboard generates 11 clock transitions (at around 20 - 30KHz) when the data is sent, and data is valid on the falling edge of the clock.

Mouse

The mouse outputs a clock and data signal when it is moved; otherwise, these signals remain at logic ‘1’. Each time the mouse is moved, three 11-bit words are sent from the mouse to the host device. Each of the 11-bit

words contains a ‘0’ start bit, followed by 8 bits of data (LSB first), followed by an odd parity bit, and terminated with a ‘1’ stop bit. Thus, each data transmission contains 33 bits, where bits 0, 11, and 22 are ‘0’ start bits, and bits 11, 21, and 33 are ‘1’ stop bits. The three 8-bit data fields contain movement data as shown below. Data is valid at the falling edge of the clock, and the clock period is 20 to 30KHz.

The mouse assumes a relative coordinate system wherein moving the mouse to the right generates a positive number in the X field, and moving to the left generates a negative number. Likewise, moving the mouse up generates a positive number in the Y field, and moving down represents a negative number (the XS and YS bits in the status byte are the sign bits – a ‘1’ indicates a negative number). The magnitude of the X and Y numbers represent the rate of mouse movement – the larger the number, the faster the mouse is moving (the XV and YV bits in the status byte are movement overflow indicators – a ‘1’ means overflow has occurred). If the mouse moves continuously, the 33-bit transmissions are repeated every 50ms or so. The L and R fields in the status byte indicate Left and Right button presses (a ‘1’ indicates the button is being pressed).

Mouse status byte X direction byte Y direction byte

L R 0 1 XS YS XY YY P X0 X1 X2 X3 X4 X5 X6 X7 P Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 P10 100 11

Stop bit

Idle state

Start bit Stop bit

Start bit

Stop bit

Start bit

VGA Port

VGA "DB15" Connector

The five standard VGA signals Red (R), Green (G), Blue (B), Horizontal Sync (HS), and Vertical Sync (VS) are routed directly to the VGA connector, bypassing the CPLD. A 270ohm series resistor is used on each color signal. This resistor forms a divider with the 75ohm VGA cable termination, resulting in a signal that conforms to the VGA specification (i.e., 0V for fully off and .7V for fully on).

VGA signal timings are specified, published, copyrighted and sold by the VESA organization (www.vesa.org). The following VGA system

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GND

270

B HS

DIO5 Reference Manual Digilent, Inc.

timing information is provided as an example of how a VGA monitor might be driven in 640 by 480 mode. For more precise information, or for information on higher VGA frequencies, refer to document available at the VESA website (or experiment!).

VGA system timing

CRT-based VGA displays use amplitude modulated, moving electron beams (or cathode rays) to display information on a phosphorcoated screen. LCD displays use an array of switches that can impose a voltage across a small amount of liquid crystal, thereby changing light permitivity through the crystal on a pixel-by-pixel basis. Although the following description is limited to CRT displays, LCD displays have evolved to use the same signal timings as CRT displays (so the “signals” discussion below pertains to both CRTs and LCDs).

CRT displays use electron beams (one for red, one for blue and one for green) to energize the phosphor that coats the inner side of the display end of a cathode ray tube (see drawing below). Electron beams emanate from “electron guns”, which are a finely pointed, heated cathodes placed in close proximity to a positively charged annular plate called a “grid”. The electrostatic force imposed by the grid

pulls away rays of energized electrons as current flows into the cathodes. These particle rays are initially accelerated towards the grid, but they soon fall under the influence of the much larger electrostatic force that results from the entire phosphor coated display surface of the CRT being charged to 20kV (or more). The rays are focused to a fine beam as they pass through the center of the grids, and then they accelerate to impact on the phosphor coated display surface. The phosphor surface glows brightly at the impact point, and the phosphor continues to glow for several hundred microseconds after the beam is removed. The larger the current fed into the cathode, the brighter the phosphor will glow.

Between the grid and the display surface, the beam passes through the neck of the CRT where two coils of wire produce orthogonal electromagnetic fields. Because cathode rays are composed of charged particles (electrons), they can be deflected by these magnetic fields. Current waveforms are passed through the coils to produce magnetic fields that interact with the cathode rays and cause them to transverse the display surface in a “raster” pattern, horizontally from left to right and vertically from top to bottom. As the cathode ray moves over the surface of the display, the current sent to the electron guns can be increased or decreased to change the brightness of the display at the cathode ray impact point.

Anode (entire screen)

Cathode ray tube

Deflection coils

Cathode ray

Cathode ray tube display system

Grid

Electron guns (Red, Blue, Green)

R,G,B signals (to guns)

gun

deflection

control

High voltage supply (>20kV)

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grid

control

Control board

control

Sync signals (to deflection control)

VGA cable

DIO5 Reference Manual Digilent, Inc.

Information is only displayed when the beam is moving in the “forward” direction (left to right and top to bottom), and not during the time the beam is reset back to the left or top edge of the display. Much of the potential display time is therefore lost in “blanking” periods when the beam is reset and stabilized to begin a new horizontal or vertical display pass.

The size of the beams, the frequency at which the beam can be traced across the display, and the frequency at which the electron beam can be modulated determine the display resolution. Modern VGA displays can accommodate different resolutions, and a VGA controller circuit dictates the resolution by producing timing signals to control the raster patterns. The controller must produce synchronizing pulses at 3.3V (or 5V) to set the frequency at which current flows through the deflection coils, and it must ensure that video data is applied to the electron guns at the correct time. Raster video displays define a number of “rows” that corresponds to the

number of horizontal passes the cathode makes over the display area, and a number of “columns” that corresponds to an area on each row that is assigned to one “picture element” or pixel. Typical displays use from 240 to 1200 rows, and from 320 to 1600 columns. The overall size of a display, and the number of rows and columns determines the size of each pixel.

Video data typically comes from a video refresh memory, with one or more bytes assigned to each pixel location (the DIO5 board uses 3-bits per pixel). The controller must index into video memory as the beams move across the display, and retrieve and apply video data to the display at precisely the time the electron beam is moving across a given pixel.

A VGA controller circuit must generate the HS and VS timings signals and coordinate the delivery of video data based on the pixel clock. The pixel clock defines the time available to display 1 pixel of information. The VS signal defines the “refresh” frequency of the display, or

Current through horizontal defletion coil

time

pixel 0,0

640 pixels are displayed each time the beam travels across the screen

pixel 0,639

VGA display

surface

pixel 479,0 pixel 479,639

Stable current ramp - information displayed during this time

Total horizontal time

Horizontal display time

Retrace - no information displayed during this time

retrace

time

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Horizontal sync signal sets retrace frequency

"back porch""front porch"

DIO5 Reference Manual Digilent, Inc.

the frequency at which all information on the display is redrawn. The minimum refresh frequency is a function of the display’s phosphor and electron beam intensity, with practical refresh frequencies falling in the 50Hz to 120Hz range. The number of lines to be displayed at a given refresh frequency defines the horizontal “retrace” frequency. For a 640pixel by 480-row display using a 25MHz pixel clock and 60 +/-1Hz refresh, the signal timings shown in the table below can be derived. Timings for sync pulse width and front and back porch intervals (porch intervals are the pre- and post-sync pulse times during which information cannot be displayed) are based on observations taken from VGA displays.

Symbol Parameter

Sync pulse time

Display time

disp

VS pulse width

VS front porch

VS back porch

Vertical Sync

Time Clocks Lines

16.7ms

15.36ms

320 us 928 us

64 us

416,800 384,000

1,600 8,000

23,200

521 480

2 10 29

A VGA controller circuit decodes the output of a horizontal-sync counter driven by the pixel clock to generate HS signal timings. This counter can be used to locate any pixel location on a given row. Likewise, the output of a vertical-sync counter that increments with each HS pulse can be used to generate VS signal timings, and this counter can be used to locate any given row. These two continually running counters can be used to form an address into video RAM. No time relationship between the onset of the HS pulse and the onset of the VS pulse is specified, so the designer can arrange the counters to easily form video RAM addresses, or to minimize decoding logic for sync pulse generation.

Horizontal Sync

Time

32 us

25.6 us

3.84 us 640 ns

1.92 us

Clocks

800 640

96 16 48

disp

XCR3128XL CoolRunner CPLD

The CPLD is in a TQ144 package that has 108 user I/Os available. Of these, 63 are routed to devices on the DIO5, 17 are assigned to form a “system bus” that connects the DIO5 and a system board, 10 connect pushbutton signals directly to a system board, 6 are uncommitted I/O signals routed to the system board, and 2 are used to pass PS/2 port signals through to a system board. The remaining 10 signals are not connected. CPLD pinouts are shown in the table below.

The CPLD can contain various controller circuits to pass DIO5 device signals to an attached system board. During manufacturing, the CPLD is configured with the register-based circuit shown in the Appendix, but the CPLD can easily be configured with other circuits.

JTAG programming signals are routed across the expansion connectors from the D2-SB, D2FT, and other system boards, so the CPLD can be configured whenever the DIO5 is attached to one of these boards. The CPLD will appear in the scan chain when shorting blocks are loaded on pins 1 & 2 of jumpers JP2 & JP3 (conversely, if shorting blocks are loaded on pins 2 and 3, the CPLD will not appear in the scan chain). The center pins of JP2 & JP3 should not be left floating – jumpers should always be loaded across pins 1 & 2 or across pins 2 & 3.

Expansion Connectors

The connector pinouts are shown below. Separately available tables show pass-through connections for the devices on the DIO5 board when it is attached to various system boards.

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DIO5 Reference Manual Digilent, Inc.

XCR3128XL CPLD Pinout for DIO5 board

Pin # Signal Dir Pin # Signal Dir Pin # Signal Dir Pin # Signal Dir

1 LCDRW out 37 LD7 out 73 2 LCDRS out 38 LD8 out 74 ADR0 in 110 BCOD1 in 3 4 5 IO-02 open 41 LDB out 77 DB0 bidi 113 BOUTA in 6 IO-01 open 42 LDC out 78 ADR1 in 114 BOUTB in 7 KDIN in 43 NC 79 DB1 bidi 115 8 KCIN in 44 LDD out 80 ADR2 in 116 BOUTC in

9 DSPA1 out 45 LDE out 81 DB2 bidi 117 BOUTD in 10 DSPA2 out 46 LDF out 82 ADR3 in 118 BOUTE in 11 DSPA3 out 47 NC 83 DB3 bidi 119 BOUTF in 12 DSPA4 out 48 NC 84 ADR4 in 120 KCLK out 13 14 DSPDP out 50 15 DSPCG out 51 16 DSPCF out 52 17 18 DSPCE out 54 BTN8 in 90 DB6 bidi 126 CLK2 in 19 NC 55 BTN9 in 91 OE in 127 LCLK in 20 21 DSPCD out 57 22 DSPCC out 58 23 DSPCB out 59 24 25 DSPCA out 61 BTN5 in 97 SW6 in 133 IO-05 open 26 LD0 out 62 BTN6 in 98 SW5 in 134 LCDDB0 bidi 27 LD1 out 63 BTND in 99 SW4 in 135 28 LD2 out 64 29 LD3 out 65 BTN1 in 101 SW2 in 137 LCDDB2 bidi 30 LD4 out 66 BTN2 in 102 SW1 in 138 LCDDB3 bidi 31 LD5 out 67 BTN3 in 103 NC 139 LCDDB4 bidi 32 LD6 out 68 BTNE in 104 33 34 NC 70 BTNA in 106 IO-06 open 142 LCDDB7 bidi 35 NC 71 BTNB in 107 LCDEN out 143 LCD-EN out 36 NC 72 BTNF in 108 NC 144

GND

TDI

PORTEN

GND

TMS

VCC33

GND

39 LD9 out 75 NC 111 BCOD2 in 40 LDA out 76

49 NC 85

VCC33 VCC33

GND

53 BTN7 in 89

56 BTNC in 92 DB7 bidi 128 LCLK in

GND

VCC33

GND

60 BTN4 in 96 SW7 in 132 IO-04 open

GND

69 BTN0 in 105

86 DB4 bidi 122 NC 87 ADR5 in 123 88 DB5 bidi 124

93 CS in 129 94 SW8 in 130 95

100 SW3 in 136 LCDDB1 bidi

VCC33

GND

TCK

VCC33

TDO GND

109 BCOD0 in

112 BCOD3 in

121 KDAT out

125 WE in

131 IO-03 open

140 LCDDB5 bidi 141 LCDDB6 bidi

VCC33

GND

VCC33

GND

VCC33

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DIO5 Reference Manual Digilent, Inc.

DIO5 Expansion Connector Pinout

P1 Signal Dir P2 Signal Dir

1 2 3 4 5 nc 5 nc 6 7 nc 7 nc 8 nc 8 nc 9 nc 9 nc

10 nc 10 IO-06 open 11 SW1 out 11 CLK2 12 nc 12 IO-05 open 13 SW3 out 13 IO-04 open 14 SW2 out 14 IO-03 open 15 SW5 out 15 IO-02 open 16 SW4 out 16 IO-01 open 17 SW7 out 17 nc 18 SW6 out 18 nc 19 LCLK in 19 KDAT out 20 SW8 out 20 KCLK out 21 DB7 bidi 21 HS in 22 CS in 22 LCLK in 23 DB6 bidi 23 BLU in 24 OE in 24 VS in 25 DB5 bidi 25 RED in 26 WE in 26 GRN in 27 DB4 bidi 27 BOUTE out 28 ADR5 in 28 BOUTF out 29 DB3 bidi 29 BOUTC out 30 ADR4 in 30 BOUTD out 31 DB2 bidi 31 BOUTA out 32 ADR3 in 32 BOUTB out 33 DB1 bidi 33 BCOD2 out 34 ADR2 in 34 BCOD3 out 35 DB0 bidi 35 BCOD0 out 36 ADR1 in 36 BCOD1 out 37 38 ADR0 in 38 LCDEN in 39 40

TDO

TDI TMS TCK

JTSEL (VCC33)

VCC33

GND

1 nc 2 nc 3 nc 4 nc

6 nc

37 39

VCC33

GND

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DIO5 Reference Manual Digilent, Inc.

Appendix 1. Default CPLD configuration

------------------------------------------------------------------------

-- DlabDio5.vhd -- Digilab DIO5 Default CPLD Configuration

------------------------------------------------------------------------

-- Author: Clint Cole

------------------------------------------------------------------------

-- This module contains the default configuration for the DIO5 XCR3128XL

-- CoolRunner CPLD. This project implements a bus-oriented, register-based

-- interface that can be used by a system board to interact with the DIO5

-- board. The 16 push buttons, 8 switches, 4 digit seven segment display, and

-- 16 discrete led's are accessed via the CPLD according to the memory map:

-- address read write

-- 000 BtnLo LedLo

-- 001 BtnHi LedHi

-- 010 Swt SsegLo

-- 010 - SsegHi

-- The sixteen buttons on the DIO5 are arranged as a decimal keypad and

-- six directly-connected function buttons. All buttons are routed through

-- the CPLD and are readable via the bus interface. Additionally, Buttons 0-9

-- are encoded to BCD by the CPLD logic. The remaining six buttons pass

-- through the CPLD and connect directly to the system board interface

-- connectors. All buttons are debounced by latches driven by the

-- input clock (signal LCLK).

-- The eight slide switches bypass the CPLD and connect directly

-- to the interface connectors, and they also pass through the CPLD to allow

-- reading via the bus interface.

-- The LCD display signals pass through the CPLD to provide logic level

-- conversion from the 5V logic levels of the LCD display to the 3.3V

-- logic levels used by system boards.

-- The VGA signals on the DIO5 board go directly to the connectors and are

-- not connected to the CPLD.

-- The keyboard signals pass through the CPLD to provide logic level

-- shifting. The standard implementation provides an input only keyboard

-- and does not support writing to the keyboard.

------------------------------------------------------------------------

-- Revision History:

-- 08/20/2003(ClintC): created

------------------------------------------------------------------------

library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity DlabDio5 is Port ( db : inout std_logic_vector(7 downto 0); adr : in std_logic_vector(5 downto 0); lclk : in std_logic; cs : in std_logic; we : in std_logic; oe : in std_logic; lcen : in std_logic; rgbLcd : inout std_logic_vector(7 downto 0); lcden : out std_logic; lcdrw : out std_logic; lcdrs : out std_logic; rgbBtnIn : in std_logic_vector(15 downto 0);

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DIO5 Reference Manual Digilent, Inc.

rgbSwt : in std_logic_vector(7 downto 0); encBtn : out std_logic_vector(3 downto 0); rgbBtnOt : out std_logic_vector(5 downto 0); rgbLed : out std_logic_vector(15 downto 0); rgbSsgAn : out std_logic_vector(3 downto 0); rgbSsgCa : out std_logic_vector(7 downto 0); kclk : out std_logic; kdat : out std_logic; kcin : in std_logic; kdin : in std_logic); end DlabDio5;

architecture Behavioral of DlabDio5 is

------------------------------------------------------------------------

-- Component Declarations

------------------------------------------------------------------------

-- Constant and Signal Declarations

------------------------------------------------------------------------

-- Internal registers for output devices signal regLed : std_logic_vector(15 downto 0); signal regSsg : std_logic_vector(15 downto 0); signal regBtn : std_logic_vector(15 downto 0); signal rgbSyncBtn : std_logic_vector(15 downto 0);

-- Other needed signals signal busDout : std_logic_vector(7 downto 0); signal cntDig : std_logic_vector(1 downto 0) := "00"; signal ssg : std_logic_vector(6 downto 0); signal dig : std_logic_vector(3 downto 0); signal an : std_logic_vector(3 downto 0);

----------------------------------------------------------------------------

-- Module Implementation

----------------------------------------------------------------------------

begin

------------------------------------------------------------------------

-- Bus drive control logic. Data bus is driven only when oe and cs are valid.

------------------------------------------------------------------------

db <= busDout when (oe = '0' and cs = '0') else "ZZZZZZZZ";

-- Output mux to place selected data on bus busDout <= rgbSyncBtn(7 downto 0) when adr = "000000" else rgbSyncBtn(15 downto 8) when adr = "000001" else rgbSwt when adr = "000010" else rgbLcd;

------------------------------------------------------------------------

-- Registers for On-Board Output Devices (LEDs and Sseg display)

------------------------------------------------------------------------

-- The WE signal is driven from a global clock buffer. process (we) begin if (we'event and we = '1') then if (adr = "000000" and cs = '0') then regLed( 7 downto 0) <= db; end if; if (adr = "000001" and cs = '0') then regLed(15 downto 8) <= db; end if; if (adr = "000010" and cs = '0') then regSsg( 7 downto 0) <= db; end if;

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DIO5 Reference Manual Digilent, Inc.

if (adr = "000011" and cs = '0') then regSsg(15 downto 8) <= db; end if; end if; end process;

-- Assign outputs of the LED holding registers to the led outputs rgbLed <= not regLed;

------------------------------------------------------------------------

-- Synthesize control signals for the LCD display

------------------------------------------------------------------------

rgbLcd <= db when (cs = '0' and we = '0') else "ZZZZZZZZ"; lcden <= '1' when (adr = "0001--" and cs = '0' and not ((we = '1') and (oe = '1'))) or lcen = '1' else '0'; lcdrw <= we; lcdrs <= adr(0);

------------------------------------------------------------------------

-- Get button inupts: All 16 button inputs are registered. Six buttons

-- (A through F) are passed directly through to output pins on the CPLD,

-- and ten buttons (0 through 9) are encoded to BCD.

------------------------------------------------------------------------

-- Register all buttons process(rgbBtnIn, lclk) begin if lclk = '1' and lclk'Event then regBtn <= rgbBtnIn; end if; end process; rgbSyncBtn <= regBtn;

-- Assign debounced pass-through buttons to their outputs rgbBtnOt <= rgbSyncBtn(15 downto 10);

-- 10-4 Line BCD Encoder for Buttons encBtn <= "0000" when rgbSyncBtn(0) = '1' else "0001" when rgbSyncBtn(1) = '1' else "0010" when rgbSyncBtn(2) = '1' else "0011" when rgbSyncBtn(3) = '1' else "0100" when rgbSyncBtn(4) = '1' else "0101" when rgbSyncBtn(5) = '1' else "0110" when rgbSyncBtn(6) = '1' else "0111" when rgbSyncBtn(7) = '1' else "1000" when rgbSyncBtn(8) = '1' else "1001" when rgbSyncBtn(9) = '1' else "1111";

------------------------------------------------------------------------

-- Seven Segment Display Driver

------------------------------------------------------------------------

-- Counter to cycle around the four digit numbers. process (lclk) begin if lclk = '1' and lclk'Event then cntDig <= cntDig + 1; end if; end process;

-- Seven Segment Display Decoder. This logic defines a four bit binary to

-- seven segment decoder. The output produces a logic 1 for each segment

-- that should be on and a logic 0 for each segment that should be off.

-- Segment A is the least significant bit.

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DIO5 Reference Manual Digilent, Inc.

ssg <= "0111111" when dig = "0000" else "0000110" when dig = "0001" else "1011011" when dig = "0010" else "1001111" when dig = "0011" else "1100110" when dig = "0100" else "1101101" when dig = "0101" else "1111101" when dig = "0110" else "0000111" when dig = "0111" else "1111111" when dig = "1000" else "1101111" when dig = "1001" else "1110111" when dig = "1010" else "1111100" when dig = "1011" else "0111001" when dig = "1100" else "1011110" when dig = "1101" else "1111001" when dig = "1110" else "1110001" when dig = "1111" else "0000000";

-- Digit multiplexor. The anode for each digit in enabled

-- in succession, and the appropriate cathode data is muxed onto

-- the cathode lines while the corresponding anode is driven. an <= "1110" when cntDig = "00" else "1101" when cntDig = "01" else "1011" when cntDig = "10" else "0111" when cntDig = "11" else "1111";

dig <= regSsg(15 downto 12) when cntDig = "00" else regSsg(11 downto 8) when cntDig = "01" else regSsg( 7 downto 4) when cntDig = "10" else regSsg( 3 downto 0);

-- Map the internal signals to the pins on the CPLD. rgbSsgAn <= an; rgbSsgCa <= '1' & (not ssg);

kclk <= kcin; kdat <= kdin;

end Behavioral;

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Digilent DIO5 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual