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Technical
Support  Communications
at a Glance
Notes
on Boot-Up sequence of Servida Motors with regard to communications:
They default to 9600 Baud, no parity 8 data bits and 1 stop bit.
(9600,N,8,1). All Servida
Motors boot up in ECHO_OFF mode with no address.
This means they will respond to globally addressed commands,
i.e. commands proceeded by nothing, or a dec128 (or hex80). Within the first 200msec’s or so of power
up, if they have not received any serial communications, they will
begin executing code previously downloaded to them from the top
down. If the Code begins with RUN? , execution
will stop at that line until a “RUN” is received via RS-232 serial
port.
Multiple
motors on a communications line
If multiple motors
are to be placed on a communications line, they must be set up properly
to avoid communications errors.
RS-232
If RS-232 is used from
a host PC or other RS-232 compatible device, all motors must be
in ECHO mode. While in ECHO
mode, all data reaching a motor’s received port will be “echoed”
back out it’s transmit port. Since
RS-232 serial lines must be daisy-chained together, the motors must
be in ECHO mode to work properly.
An RS-232 chain of motors can be addressed from a host or
master without the motors containing programs.
RS-485
If RS-485 is used,
all motors must be in ECHO-OFF mode. RS-485 is a parallel communications network.
If any motor was to echo out commands received, it would
cause all motors or any other devices on the network to get hit
with the same data. An RS-485
chain requires each motor to have an internal program with a unique
address.
Note: Servida Motors
use 2 wire RS-485 standards. This means line biasing determines
whether or not the motor is in transmit mode or receive mode at
the hardware level. To insure
motors do not hang up in the transmit mode, there must be a minimum
of a 200mVolt differential between RS-485 A and B channels. This is easily achieved by placing a pull
down resistor of about 500 Ohms from the B channel to ground somewhere
on the RS-485 network. All
Servida Motors have a 5Kohm pull-up resistor on both A and B channels
already. The 500 Ohm resistor will provide the enough biasing needed
to make the hardware default to the receive state.
If there are long distances between motors, it may be necessary
to provide a resistance across channels A and B.
A 200 Ohm resistor wired from A to B at the remote end of
the RS-485 line should provide ample voltage drop for the needed
biasing. If the above electrical rules are not applied, communications
cannot be guaranteed to work.
Pre-Addressed
Motors on Boot-Up
If it is desired for
the motor to have an address on boot-up, the motor must have a program
downloaded to it with the set address command at or near the top
of the program.
Example:
SADDR1 will
set the motor’s address to 1.
The motor address command uses integer numbers 1-120, however to
specifically address a particular Servida Motor, you must precede the
desired command with decimal or hex equivalent addresses with an
offset of dec128.
Example: If a motor’s program begins with SADDR1, then a
command specifically meant for that motor must be preceded by dec129
or hex81.
Example: To set commanded velocity on motor 1 to 1000 you
would transmit the following: hex81V=1000
To set commanded acceleration on motor 2 to 500 you would transmit
the following:
hex82A=500
The commands must be followed by either a carriage return or space
character (dec13 or dec10).
These same rules apply to one Servida Motor talking to another. Once an address has been transmitted, it
need not be transmitted again with additional commands until it
is time to change the address.
Addressed commands can be sent out by Servida Motors as well
as host computers via use of the PRINT commands in proper format.
Example: PRINT(#131,”A=1200”,#13)
The above code sends out dec131 immediately followed by A=1000 immediately
followed by a carriage return.
PRINT(#131,”A=1200 “) would give the same result because
a space was included after A=1200, and a space counts as a delimeter.
Global
addressing:
As mentioned at the
beginning, all motors without an address respond to any command preceded
by dec128 or hex80. This is
also true for any motor with an address that is not in “sleep” mode.
If a motor is in Sleep mode, it will only start listening again
if the WAKE command preceded by its address is sent to that motor.
Example:
If hex85SLEEP is transmitted, motor
5 will go into “sleep mode.”
If hex80x=123 is transmitted, every
motor on the serial line will have
variable x updated to 123
except motor 5.
If hex85WAKE is transmitted, motor 5
will “wake up”
and will respond once again
to commands.
Addressed
or De-Addressed state:
It is important to
understand addressed or de-addressed states of Servida Motors.
These states determine whether or not a Servida Motor will respond
to commands. Lets assume for example that we have 5 motors
on a communications network. All
of them have programs downloaded with addresses 1-5 respectively via
the SADDR command. On Boot-up
all are ready to listen. They will respond to either a globally addressed
command or a specific motor will respond to a specifically addressed
command. Once a specific address is sent out on the
line, that motor will remain in the “addressed” state. All other motors will be in the “de-addressed”
state. What this means is
that from that point on, any command sent out to the motors without
an address proceeding it, will be acted upon only by the motor in
the addressed state. All other
motors will basically ignore anything received.
By sending out a command preceded by the global address (hex80
or dec128), all motors will be placed into the “addressed” state and
will remain in that state until another specific address is transmitted. Under this case of 5 motors addressed 1-5
respectively, if a hex89 for example or any other address outside
of hex80-hex85 is sent, all motors would become “de-addressed”. No motor would respond to any command until an address within
the range of motors on the line is received.
This does come in handy if other Non-Servida Motor devices are
on the same network.
For example: suppose you have the same 5 Servida Motors on line
with a barcode reader or temperature controller.
If you wanted to send set-up parameters to these devices but
wanted to insure the Servida Motors would ignore the set-up parameters
(since they are more than likely not even valid Servida Motor syntax),
you could “de-address” all Servida Motors by sending out an address outside
the bounds of any motor on the line.
Most RS-485 devices operate this way.
Addressing
Servida Motors from a Host PC or other Serial Device
Note: This only applies to an RS-232 serial daisy
chain. It will not work on an RS-485 network.
Motors must be pre-addressed in downloaded programs for an
RS-485 network to work at all. It is important to realize the boot-up state
of Servida Motors from the first section to understand this sequence. Please review it if you have not already
done so.
Since Servida Motors without addresses default to address zero (hex80
or dec128), a sequence of commands must be issued in proper order
to achieve addressing of the Servida Motors.
Servida Motors without programs downloaded into them will not retain
addresses from this procedure upon loss and return of power!
The following is an example sequence of addressing 3 Servida Motors from
the SVI software terminal screen.
Assumptions are as follow:
1. Host PC is set up for 9600 Baud,N,8,1 since this is the power-up
default for Servida Motors.
2. Three Servida Motors are wired in serial daisy chain with Tx of Host
PC wired to Motor-1 Rx, Motor-1 Tx wired to Motor-2 Rx, Motor-2 Tx
wired to Motor-3 Rx, Motor-3 Tx wired to Host PC Rx.
(Tx is RS-232 transmit, Rx is RS-232 Receive)
0ECHO_OFF
0SADDR1
1ECHO
1SLEEP
0SADDR2
2ECHO
2SLEEP
0SADDR3
3ECHO
3SLEEP
1WAKE
2WAKE
3WAKE |
Places all motors in echo off
Set first motor to address 1
Set it to echo mode so the next motor will be able to receive
commands
Set it to sleep mode so it will not act upon following commands
Set next motor to address 2 and repeat sequence
Set all motors to wake status. |
Note: SVI Software automatically
replaces leading numbers in commands with a decimal offset of 128.
In other words, 0ECHO_OFF resulted in “(dec128)ECHO_OFF” being
transmitted.
This is the equivalent from any other software source:
(dec128)ECHO_OFF
(dec128)SADDR1
(dec129)ECHO
(dec129)SLEEP
(dec128)SADDR2
(dec130)ECHO
(dec130)SLEEP
(dec128)SADDR3
(dec131)ECHO
(dec131)SLEEP
(dec129)WAKE
(dec130)WAKE
(dec131)WAKE
Note: (hex80-83) is the same as (dec128-131). All lines must be terminated with either
a carriage return (dec13) or space character.
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