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GS-C200

INTELLIGENT STEPPER MOTOR CONTROLLERS

STMicroelectronics 

GS-C200 / GS-C200S

INTERFACE TO THE HOST COMPUTER AND

DATA PROTOCOL

The interface to the Host Computer is through an

RS232 or V24 serial communication port.

Baud Rate Programming

The Baud rate is programmed between 110 and

9600 bit/sec by using the BR0, BR1 and BR2 inputs

according to the following table:

BR0 (p4)

0

1

0

1

0

1

0

1

BR1 (p5)

0

0

1

1

0

0

1

1

BR2 (p6)

0

0

0

0

1

1

1

1

Baud Rate

9600

4800

2400

1200

600

300

150

110

This setting is obtained by connecting the pins 4, 5,

and 6 to ground (0 status) or by leaving them open

(1 status). The communication port does not use

any control line but just the transmit and receive

signals. The host computer must handle the data

excange in the proper way.

Module Address Programming

The communication protocol can be either Point to

Point or Multipoint. In the first case a single com-

munication line is required for each module, while

in the latter more than one module (up to seven)

can share the same communication line.

The Multipoint protocol as well as the peripheral

device address are selected through SEL0, SEL1

and SEL2 inputs. The Point-to-Point protocol is

selected by connecting all the SEL inputs to the 5V

output pin (pin 20) or by leaving them open.

The following table defines the protocol and the

address setting:

SEL2

0

1

0

1

0

1

0

1

SEL1

0

0

1

1

0

0

1

1

SEL0

0

0

0

0

1

1

1

1

Address

7

6

5

4

3

2

1

–

Protocol

Multipoint

Multipoint

Multipoint

Multipoint

Multipoint

Multipoint

Multipoint

Point-to-Point

When the multipoint connection is chosen, the ad-

dress of each module is obtained by connecting the

various SEL pin (1, 2, 3) to ground (0 status) or by

leaving them open (1 status).

The basic difference between the two protocols is

represented by the sytem wiring complexity and the

data throughput. The Point-to-Point offers the

higher throughput data rate but it requires a con-

necting cable for each unit, while the Multipoint

minimizes the connecting cables but at reduced

throughput rate. When this latter protocol is chosen,

the command must always be preceeded by the

address of the unit.

Data Exchange Protocol

The dialogue is always driven by the Host Com-

puter which sends the string containing the com-

mand or the request to be implemented. The GS-C

module stores the instruction sent by the Host and

then it checks if the string has been correctly re-

ceived by analyzing the parity bit. It then analyzes

the consistency of the received instructions by veri-

fying the presence and correctness of the argu-

ment, and finally, it checks whether the request can

be processed or not (for example, an attempt to

move outside the system limits, etc.) reporting to

the Host the analisys result. If no error is detected,

the GS-C replies to the Host by a ”Y” message. In

case of error, the message will be ”Error X” request-

ing the Host to send the message again or to modify

some parameters of the previous message to fix the

error detected by the GS-C. The actual value of X

(see fig. 4 and error code table) gives the Host the

information on the type of detected error. The pro-

cedure implemented for the dialogue with the Host

is shown on the flowchart of fig. 4.

Figure 4. Controller-Host Dialogue Flowchart.

9/31

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