page
1
phone: 360.260.2468
l
sales: 800.736.0194
l
fax: 360.260.2469
email: sales@usdigital.com
l
website: www.usdigital.com
11100 ne 34th circle
l
vancouver, washington 98682 USA
SEI
Serial Encoder Interface Bus
US
Digital
C o r p o r a t i o n
TM
US Digital's SEI bus is a simple, quick and convenient way of networking devices
to an RS232 serial port.
The AD2-B adapter is available to interface to a standard RS232 port (9-pin DSUB)
such as those in PCs. For the 25-pin version please see the AD2-A data sheet. A
wall-mount power supply furnishes the power for all devices on the SEI bus.
Description:
The SEI bus can support 1 to 15 devices on the SEI bus. The network configuration can be a chain, star, or a combination of both and does not require cable
terminations.
The bidirectional data lines carry commands from the host computer and responses from the device(s). The format is 1 start bit, 8 data bits and 1 stop bit.
The baud rate can be changed, but it always starts as 9600 baud after reset or power up. Since the data bus is bidirectional, the host must release the bus
within 20 uSec after the last command byte to avoid contention with the device's response. The AD2-B adapter does this automatically and biases these lines
with pull-up/down resistors to keep them in the inactive state (dataL with a resistor to +5V, dataH with a resistor to ground) when the bus is idle.
The busy lines are used for flow control. When a device is busy, it activates these lines in an open collector fashion by driving busy- low and busy+ high.
They need to be biased at the host with pull-up/down resistors to keep them in the inactive state (busy+ with a resistor to ground, busy- with a resistor to
+5V) when they are not driven. They are driven by the device which has been addressed as an acknowledgment of the command. They stay active until
the command is completed. While a device drives the busy line, all other devices on the bus ignore the data flow. If a single device is on the bus, the busy
lines can be ignored and pulled to the inactive state, but it is easier to communicate with it if they are connected.
The maximum cable length from the AD2-B to any device should be limited to 1000 feet. If the baud rate used is higher than 19.2 kbaud, the length should be
reduced proportionally, ie: 200 ft at 115 kbaud. Contact us for information about longer cables at high baud rates. The power supply requirement is 5.5 volts
min., which should be considered carefully when long cables are used, because of the voltage drop caused by the cable's resistance (a typical 26 AWG
telephone cable is 40 Ohms per 1000 feet). For example, the AD2-B adapter provides 8 volts worst case. Unless power is supplied at several points along
the cable, each network branch from the AD2-B should be limited in length depending on how many devices it supports. See table above.
Up to 15 devices on a single 6-pin telephone-type cable.
Uses standard PC data rates up to 115 Kbaud.
Software & source code avaliable.
Rugged, simple, low cost.
US Digital warrants its products against defects in materials &
workmanship for two years. See complete warranty for details.
Features:
Interface:
PS-9V
AD2-B
Adapter
USD-SW
Software
To Computer
SEI-M1
General I/O Module
AD5 Quadrature Encoder to SEI Adapter
A2 Absolute Encoders
ED2 Digital Readout
TM
US Digital's
SEI Bus
Cable Distance from AD2-B Adapter:
Devices
26 AWG cable
28 AWG cable
1
1000 ft
1000 ft
2
1000 ft
640 ft
3
670 ft
420 ft
5
400 ft
250 ft
10
200 ft
125 ft
15
125 ft
80 ft
Caution: Do not use voice type telephone cables; they com-
monly reverse the pinout (it will not destroy the device, but it
will not work). The device network requires six wires straight
(pin 1 to pin 1). We offer cables (26 AWG) of any length.
Parameter
Min.Max. Units
Operating temperature
0
45
C
Humidity (non-condensing)
0
95
%
Supply voltage (PWR)
0
16
Volts
ESD warning: Normal handling precautions should be taken to avoid
static discharge.
Absolute Maximum Ratings:
page
2
phone: 360.260.2468
l
sales: 800.736.0194
l
fax: 360.260.2469
email: sales@usdigital.com
l
website: www.usdigital.com
11100 ne 34th circle
l
vancouver, washington 98682 USA
SEI
Serial Encoder Interface Bus
US
Digital
C o r p o r a t i o n
TM
Pin
Name
Description
1
GND
Ground, common for power, data and busy pairs.
2
Busy+
Bidirectional differential acknowledge line, active high (open source output, must be pulled down to ground).
Analog+
Analog version: positive analog voltage output. *A2 analog option only.
3
Busy-
Bidirectional differential acknowledge line, active low (open drain output, must be pulled up to +5 Volt).
Analog-
Analog version: analog signal ground, connected to GND pin. *A2 analog option only.
4
PWR
Power supply input.
5
DataL
Bidirectional differential data line, non-inverted (tri-state output, must be pulled up to +5 Volt).
6
DataH
Bidirectional differential data line, inverted (tri-state output, must be pulled down to ground).
Functional Pin Description:
Symbol
Description
Min.Max.Units
Note
TBH
Host command to busy active
0.01
1
mSec
1
TR1
Device response time (1 byte command)
0.01
1
mSec
TR2
Device response time (Mult. byte command)
0.01
30
mSec
2
TBL
Busy release time
0.01
0.1
mSec
TH1
Host response time
0
300
mSec
3
Notes:
1) After reset and other commands that have a longer recovery time, this timing can exceed the maximum,
or the byte may even be ignored. See command descriptions for details.
2) Commands that access the on-board EEPROM to store new parameters can take up to this time limit;
however, most commands are much shorter.
3) When the device is waiting for data from the host, it times out & aborts the command after 300 to 350
msec. (A2 rev 1.01 firmware: 30-35 msec).
AC Characteristics:
1) The lines busy+ and busy- are differential, but they should not be terminated. They should be biased at the host with pull-up/down resistors to keep them
in the inactive state when they are not driven, busy+ with 330-2200 Ohms to ground & busy- with 330-2200 Ohms to +5V. Use 2200 Ohm resistors if only
one device is on the SEI bus, use less resistance if there are more devices.
2) The lines dataL and dataH are RS485-type differential lines. They don't need to be terminated for cables up to 1000 ft long at 19.2 kbaud (proportionally
shorter at higher baud rates, i.e. 200 ft at 115 kbaud). They should be biased at the host with pull-up/down resistors to keep them in the idle state when the
bus is not driven. The recommended pull-up/down resistors are: dataL with 330-2200 Ohms to +5V, dataH with 330-2200 Ohms to ground. The resistance
is dependent on the number of devices on the SEI bus. If terminated, make sure the lines are biased such that dataL is above dataH by at least 2 volts.
3) For implementations with long cables or several devices on the bus, the supply voltage at the host should be appropriately higher to compensate for voltage
losses in the wires.
4) See the SEI-UPS uninterruptable power supply for the SEI bus data sheet for information on retaining power to SEI devices after a power failure.
General Notes:
Technical Data, Rev. 08.23.00, August 2000
All Information subject to change without notice.
Parameter
Min.
Typ.Max.Units
Notes
Supply voltage (PWR)
5.5
-
16
Volts
Differential output voltage
2
-
10
Volts
Load = 100 Ohms
|DataL - DataH| , |Busy+ - Busy-|
Differential input voltage
0.2
-
14
Volts
|DataL - DataH| , |Busy+ - Busy-|
Common mode output voltage
-
2.5
3
Volts
Load = 100 Ohms
(DataH+DataL)/2, (Busy-+Busy+)/2
Common mode input voltage
-7
-
12
Volts
(DataH+DataL)/2, (Busy-+Busy+)/2
Input current
-0.8
-
1
mA
In = -7 to 12V
DataH , DataL , Busy- , Busy+
the above is for over operating temperature range.
typical values are specified at Vcc=12V & 25C.
DC Electrical Characteristics:
Single byte command diagram
Multiple byte command diagram
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