Display Interface Types

Display Interface Types

Most displays come with a choice of interface that can be purchase separately or fitted to the chosen display. This page explains the differences between the interfaces available.

Serial options chart

See below for a more detailed explanation. NOTE the interface options also apply to other devices not just displays.

ASI-V2

This interface is addressable and so many devices can be connected to the same serial bus without any additional wires. All data sent to the device is in the form of a command. To turn on the back light of a display for example would require ‘ab1’ where ‘a’ is the device address, ‘b’ is the command for back light and ‘1’ is for on. If two or more devices were on the same bus then the second device could be addressed by ‘b’. In addition to this there are commands that reveal what addressed devices are connected to the bus.

Advantages
The main advantage for this interface is that more then one device can be used on the same bus.

Disadvantages
More complex to use and the commands are limited to the basics required for the device, no built in scrolling.

online icon Web site dedicated to BV serial devices
online icon External Link - PicAxe Basic to create custom characters on the 20 x 4 display using this interface

VT100-a

This has the same electrical interface as the ASI-V2 devices, however the command set is based on VT100. This makes the device much easier to use, on a display any data sent to the interface will be reflected on the display.

Advantages
Much easier to use, if the device is a display it will wrap at the end of a line and scroll when reaching the bottom of the display.

Disadvantages
Only one device can be on the bus at a time.

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DUAL

Dual is simply a combination of VT100 and I2C on the same device. The user chooses which interface at start up. I2C is chosen by holding the SDA line high at reset. This of course is done automatically if an I2C bus is connected because of the pull up resistors required on the I2C bus. VT100 is selected by not connected the I2C bus.

VT100

This interface is normally part of a dual interface but not always. It will not accept RS232 voltage levels but multiple devices can exist on the same bus by the use of a device deselect line. This line when active will disable the device allowing two or more devices to be used on the same bus.

Advantages
Comprehensive VT100 command set which is generally easy to use, all data sent goes to the device and commands are initiated by escape codes.

Disadvantages
If using multiple devices then each device requires a deselect input

online icon Web site dedicated to BV serial devices

I2C

I2C is a short range bus with a special protocol allowing transmit and receive using a master / slave protocol. All devices will be salve and the address can be changed by the user.

Advantages
Well known interface allowing multiple devices on the same bus. No need for a UART in the master.

Disadvantages
The host needs to have a master I2C interface that may not always be available.

on line icon Web site dedicated to BV I2C devices

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