INDUSTRIAL AUTOMATION Tip027BB TOPIC: How to Use Freeport Mode to Connect Several S7-200 CPUs in a Remote I/O Network VERSION: 4.0 DATE: 1/99 ***SPECIAL HARDWARE REQUIREMENTS*** Two or more SIMATIC S7-200 CPUs: CPU 212 or CPU 214 One connection cable, 9-pin If more than two PLCs are used (more than one slave), you will need a Siemens network bus connector. ***OVERVIEW*** In this example, three SIMATIC S7-200 CPUs are connected. Each one is a CPU 214. Station 0, called the master, is linked to stations 1 and 2, called the slaves. The master station sends four bytes of output data to each station in turn. As a result, each station responds with four bytes of input data. The Freeport communication mode is used for the data transmission. Two memory buffers are reserved: one for remote inputs and one for remote outputs. The output data that is to be transmitted is captured by moving a double word value from the output buffer to the Transmit buffer. After transmitting, the master station receives the response of the slaves and stores the data in the Receive buffer. This program includes several timed interrupt routines. Each timed interrupt routine is called by one of the following two interrupt events: interrupt event 10 and event 11. For example, in this program, interrupt event 10 calls timed interrupt routines INT0, INT1, and INT2. At one point in the program, interrupt event 11 calls INT15. The time interval for a timed interrupt routine that is called by event number 10 is specified in special memory byte SMB34. The time interval for the timed interrupt that is called by event number 11 is specified in special memory byte SMB35. In both cases, the time interval is fixed in increments of 1 ms. The smallest value permitted for the time interval is 5 ms. The largest value permitted for the time interval is 255 ms. In this program, the time interval specified in both SMB34 and SMB35 is 5 ms. It is also possible to use the Network Read (NETR) and Network Write (NETW) instructions to link a CPU 214 to other S7-200 CPUs in the Point-to-Point Interface (PPI) mode. In the PPI mode, it is possible to connect TD 200 units and operator panels (OPs) to the network and still link the stations together. ***PROGRAM STRUCTURE: SLAVE*** The program consists of the following routines: Main SBR0 SBR1 INT0 INT1 INT2 INT10 INT11 INT12 INT13 INT14 INT15 Initialize the program. Enable the Freeport mode and the quiet line timer and receiver, and set the time-out and delay time. Disable the Freeport communication mode and detach the interrupts for receiving, transmitting and timing. Enable the reception of input data (quiet line timer). Stop the timer and the transmitter (Transmit time-out timer). Enable the quiet line timer and the quiet line receiver (message time-out timer). Enable quiet line timer and quiet line receiver (transmitter interrupt). Receive the first character of a message. Receive the output data. Receive the frame check sequence (FCS) character. Enable the quiet line receiver. Enable the delayed transmitter interrupt. ***PROGRAM DESCRIPTION: SLAVE*** This program enables you to connect two, three, or more SIMATIC S7-200 CPUs (CPU 214 or CPU 212) as a communication network. The universal asynchronous receiver-transmitter (UART) is initialized as follows: odd parity PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION 8 bits per character 38,400 baud (CPU 214) 19,200 baud (CPU 212) If you use only SIMATIC CPU 214 PLCs, the application runs at 38,400 baud. If you use only SIMATIC CPU 212 PLCs, the application runs automatically at 19,200 baud. If you use a combination of SIMATIC CPU 214 and CPU 212 PLCs, you need to adjust the program slightly: just change the setting of the value of special memory byte SMB30 from the hexadecimal value C0 (16#C0) to C4 (16#C4) and from the hexadecimal value C1 (16#C1) to C5 (16#C5). The application will run at 19,200 baud. If you use a slower baud rate, you must also change the time-out value that is loaded into special memory byte SMB34. ***FUNCTION OF THIS PROGRAM:*** Each message is validated by a frame check sequence (FCS) character that is formed by performing an Exclusive Or operation on the data bytes in the message. The remote I/O master is station 0 and may be connected to one, two, or three slave stations. If one slave station is connected, it must be station 1. If two slaves are connected, they must be stations 1 and 2. If three slave stations are connected, they must be stations 1, 2, and 3. The number of slave stations that are connected must be supplied as a parameter to the master station in variable memory byte VB0. For slave stations, the station address is stored in VB0. If you use a PC/PPI cable with a modem to connect the master and slave stations, set VB1 = 1; otherwise, set VB1 = 0. This setting provides a two-character delay between the Receive and Transmit messages. This delay is required when using the PC/PPI cable. Each slave station has an input buffer and an output buffer as follows: Input Buffer IB0 byte 0 IB1 byte 1 IB2 byte 2 IB3 byte 3 Output Buffer QB0 byte 0 QB1 byte 1 QB2 byte 2 QB3 byte 3 When the master station transmits a message, the slave station that is addressed by the master stores the output data in a Receive buffer and responds to the master's transmission by transmitting the input data in the Transmit buffer. These buffers are shown below. VB607 is a garbage location used in the generation of the Transmit checksum, or Frame Check Sequence (FCS). Transmit Buffer VB600 length VB601 address VB602 byte 0 VB603 byte 1 VB604 byte 2 VB605 byte 3 VB606 FCS VB607 xx Receive Buffer VB608 byte 0 VB609 byte 1 VB610 byte 2 VB611 byte 3 The message format is as follows: Address B0 B1 B2 B3 FCS The S7-200 Programmable Controller System Manual provides you with more information about the interrupt routines and the Transmit (XMT) instruction. ***MAIN PROGRAM***˛ PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 1 Enable a Two-Character Delay Time Load special memory bit SM0.1 to process this network in the first scan cycle only. Move the constant 1 into variable memory byte VB1 to enable the two-character delay that is required by the PC/PPI cable. SM0.1 1 Network 2 VB1 If the CPU Mode Switch Is in the RUN Position, Start Communication Load special memory bit SM0.7. (If SM0.7 is on, the mode switch of the CPU is in the RUN position, enabling you to select the Freeport communication mode.) If special memory bit SM0.7 is on, and special memory bit SM0.1 is on (indicating that this is the first scan cycle), call subroutine SBR0 to start communication. SM0.7 Network 3 SM0.1 0 If the CPU Mode Switch Is Moved to the RUN Position, Start Communication Load special memory bit SM0.7. If there is an off-to-on transition (positive or rising edge) at special memory bit SM0.7 (that is, when the CPU mode switch is moved to the RUN position), call SBR0 to start communication. SM0.7 0 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 4 If the CPU Mode Switch Is in the TERM Position, Disable Communication Load special memory bit SM0.7 as a Normally Closed contact so that power will flow if SM0.7 is not on (that is, if it has a signal state of 0). If special memory bit SM0.7 is off, the mode switch of the CPU is in the TERM position. If the mode switch is in the TERM position, call SBR1 to disable communication. SM0.7 Network 5 1 Main Program End End the main program. Network 6 Subroutine SBR0 SBR0 initializes the Freeport mode and enables the interrupts for the quiet line timer and the quiet line receiver. Start SBR0. 0 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 7 Enable Freeport Mode, Quiet Line Timer and Receiver, and Set Timers Load special memory bit SM0.0 to process this network every scan cycle. Move the hexadecimal value C1 (binary 1100 0001) into special memory byte SMB30. This bit combination configures the communication interface for Freeport mode; 38,400 baud; 8 data bits per character; and odd parity. Enable all interrupt events. Move the constant 5 into special memory byte SMB34 to set the time interval to 5 ms for the timed interrupt routines that are triggered by interrupt event 10. This is the time-out value. (Use the 5-ms value for transmission rates of 38,400 baud and 19,200 baud. Use a 10-ms value for a transmission rate of 9600 baud.) Move the constant 5 into special memory byte SMB35 to set the time interval to 5 ms for the timed interrupt routine that is triggered by interrupt event 11. This is the two-character delay time, which has a minimum of 5 ms. Attach interrupt event 10 to INT0 to enable the 5-ms quiet line timer and enable the reception of input data. Attach interrupt event 8 (Port 0: Receive character) to INT14. When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM0.0 16#C1 SMB30 5 SMB34 5 SMB35 0 10 14 8 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 8 End of Subroutine SBR0 End SBR0. Network 9 Subroutine SBR1 SBR1 disables the Freeport communication mode and detaches the interrupts for receiving, transmitting, and timing. Start SBR1. 1 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 10 Disable Communication Load special memory bit SM0.0 to process this network every scan cycle. Move the hexadecimal value C0 (binary 1100 0000) into special memory byte SMB30. This bit combination configures the communication interface for Point-to-Point Interface (PPI/slave mode) protocol; 38,400 baud; 8 data bits per character; and odd parity. (The Freeport mode is disabled.) Detach interrupt event 8 (Port 0: Receive character) from all interrupt routines to disable the Receive interrupts. Detach interrupt event 9 (Port 0: Transmit complete) from all interrupt routines to disable the Transmit interrupts. Detach interrupt event 10 (timed interrupt) from all interrupt routines to stop the timed interrupts. SM0.0 16#C0 SMB30 8 9 10 Network 11 End of Subroutine SBR1 End SBR1. PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 12 Interrupt Routine INT0 Start INT0 (the quiet line time-out timer) to enable the reception of input data. 0 Network 13 Enable Reception of Input Data Load special memory bit SM0.0 to process this network every scan cycle. Attach interrupt event 8 (Port 0: Receive character) to INT11. When a character is received at Port 0, control is transferred to INT11 to enable the reception of input data. SM0.0 11 8 Network 14 End of Interrupt Routine INT0 End INT0. Network 15 Interrupt Routine INT1 Start INT1 to detach the timed interrupts that are triggered by interrupt event 10 and the Transmit interrupts if data is transmitted or received or if the timer is retriggered. 1 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 16 Transmit Message Time-Out Timer Load special memory bit SM0.0 to process this network every scan cycle. Detach interrupt event 10 (timed interrupt) from all interrupt routines to stop the timed interrupts. Detach interrupt event 9 (Port 0: Transmit complete) from all interrupt routines to disable the Transmit interrupts. Put the CPU into the STOP mode. SM0.0 10 9 Network 17 End of Interrupt Routine INT1 End INT1. Network 18 Interrupt Routine INT2 Start INT2 to interrupt the program if the first character of a message is received. 2 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 19 Message Time-Out Timer Load special memory bit SM0.0 to process this network every scan cycle. Attach interrupt event 10 to INT0 to enable the 5-ms quiet line time-out timer. Attach interrupt event 8 (Port 0: Receive character) to INT14. When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM0.0 0 10 14 8 Network 20 End of Interrupt Routine INT2 End INT2. Network 21 Interrupt Routine INT10 Start INT10 to interrupt the program if a message is transmitted. The Transmit interrupts are disabled. The quiet line timer begins to run and the quiet line receiver is enabled. 10 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 22 Transmitter Interrupt Load special memory bit SM0.0 to process this network every scan cycle. Detach interrupt event 9 (Port 0: Transmit complete) from all interrupt routines to disable the Transmit interrupts. Attach interrupt event 10 to INT0 to enable the 5-ms quiet line time-out timer. Attach interrupt event 8 (Port 0: Receive character) to INT14. When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM0.0 9 0 10 14 8 Network 23 End of Interrupt Routine INT10 End INT10. PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 24 Interrupt Routine INT11 Start INT11 when the first character of a message is received. The message time-out timer is set. Data can be received. If there is an error, the quiet line time-out timer and the quiet line receiver are enabled. 11 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 25 Receive the First Character of a Message Load special memory bit SM3.0 as a Normally Closed contact to enable power flow if there is no parity error at Port 0 of the CPU. If there is no parity error, compare the character in SMB2 with the contents of variable memory byte VB0 (station address of the slave station). (SMB2 contains each character that is received from Port 0 or Port 1 during Freeport communication. In this example, the CPU receives the information through Port 0.) If the number in SMB2 is equal to the station number in VB0, move the constant 0 into accumulator AC0 to initialize the checksum register, move the constant 4 into accumulator AC1 to load the Receive character count, set variable memory double word VD638 to function as a pointer to variable memory byte VB608 (the first byte of the Receive buffer), and attach interrupt event 10 to INT2 to enable the message time-out timer. Attach interrupt event 8 (Port 0: Receive character) to INT12. When a character is received at Port 0, control is transferred to INT12 to enable the reception of output data. End INT11 conditionally, that is, if there is no parity error and the message is intended for this station. SM3.0 SMB2 VB0 0 AC0 +4 AC1 &VB608 2 10 12 8 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. VD638 INDUSTRIAL AUTOMATION Network 26 Enable the Quiet Line Timer and the Quiet Line Receiver If the message was not intended for this station or there was a parity error, load special memory bit SM0.0 to process this network every scan cycle. Attach interrupt event 10 to INT 0 to enable the 5-ms quiet line timer and enable the reception of input data. Attach interrupt event 8 (Port 0: Receive character) to INT14 When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM0.0 0 10 14 8 Network 27 End of Interrupt Routine INT11 End INT11. Network 28 Interrupt Routine INT12 Start INT12 to interrupt the program if data is received and there is no error. The information is stored in a buffer. The frame check sequence (FCS) can be received by another interrupt. If there is an error, the quiet line time-out timer and the quiet line receiver are enabled. 12 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 29 Receive the Output Data Load special memory bit SM3.0 as a Normally Closed contact to enable power flow if there is no parity error at Port 0 of the CPU. If there is no parity error, move the contents of special memory byte SMB2 to the location that is pointed to by VD638 (the Receive buffer). (The asterisk in front of VD638 indicates that the contents of this double word is a pointer to another location in memory, namely to the Receive buffer location). Increment the value in variable memory double word VD638 to point to the next Receive buffer location. XOR the corresponding bits of special memory word SMW1 (contains bits that, if set to 1, indicate errors) with those of accumulator AC0 and put the result in accumulator AC0. This Exclusive Or Word operation computes the checksum. Decrement the value in accumulator AC1 to decrement the Receive character count. SM3.0 SMB2 *VD638 VD638 VD638 SMW1 AC0 AC0 AC1 AC1 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 30 Enable Reception of the FCS Load special memory bit SM1.0. This bit is turned on (set to 1) by the execution of certain instructions when the result of the operation is 0. The Decrement Word (DECW) instruction affects this bit. If Network 29 indicates that four characters have been received (that is, if the result of DECW in Network 29 was 0), special memory bit SM1.0 is turned on (set to 1). If SM1.0 is on: attach interrupt event 8 (Port 0: Receive character) to INT13. When a character is received at Port 0, control is transferred to INT13 to enable reception of the FCS. End INT12 conditionally, that is, if four characters were received. SM1.0 13 8 Network 31 If a Parity Error Occurs, Enable the Quiet Line Timer and Receiver Load special memory bit SM3.0. If there is a parity error, attach interrupt event 10 to INT0 to enable the 5-ms quiet line timer. Attach interrupt event 8 (Port 0: Receive character) to INT14. When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM3.0 0 10 14 8 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 32 End of Interrupt Routine INT12 End INT12. Network 33 Interrupt Routine INT13 Start INT13 to receive the frame check sequence (FCS) character. The program does not enable any timed interrupt or any Receive interrupt. After the FCS is computed, the program enables the transmitter time-out and transmitter interrupts. If there is an error, the program enables the quiet line time-out timer and the quiet line receiver. 13 Network 34 Disable the Quiet Line Receiver and the Quiet Line Timer Load special memory bit SM0.0 to process this network every scan cycle. Detach interrupt event 8 (Port 0: Receive character) from all interrupt routines to disable the Receive interrupts. Detach interrupt event 10 (timed interrupt) from all interrupt routines to stop the timed interrupts. SM0.0 8 10 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 35 Receive the FCS Character and Save the Output Data Load special memory bit SM3.0 as a Normally Closed contact to enable power flow if there is no parity error at Port 0 of the CPU. If there is no parity error, compare the character in SMB2 with the contents of accumulator AC0. If the contents of SMB2 are equal to the FCS, move the contents of variable memory double word VD608 (the output data) to output double word QD0 (the output buffer of the slave station). Move the constant 6 into variable memory byte VB600 to indicate the length of the Transmit buffer = 6 bytes. Move the contents of variable memory byte VB0 (the slave station address) into variable memory byte VB601 (in the Transmit buffer). Move the contents of input double word ID0 (the input data of the slave station) into variable memory double word VD602 (the data bytes of the Transmit buffer). XOR the corresponding bits of variable memory word VW602 with those of VW604 to compute the frame check sequence (FCS) and put the result in accumulator AC0. Move the value in accumulator AC0 into variable memory byte VB606. XOR the corresponding bits of accumulator AC0 and variable memory word VW606 and put the result into VW606 to save the FCS. Turn on (set to 1) memory bit M0.0 to enable the Transmit bit. SM3.0 SMB2 AC0 VD608 QD0 6 VB600 VB0 VB601 ID0 VD602 VW602 VW604 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. AC0 INDUSTRIAL AUTOMATION AC0 VB606 AC0 VW606 VW606 M0.0 Network 36 Enable the Delayed Transmitter Interrupt Load memory bit M0.0. If memory bit M0.0 is on (has a signal state of 1), and the constant 1 is equal to the number in variable memory byte VB1 (that is, you are using a PC/PPI cable with a modem to connect the master and slave stations), attach interrupt event 11 to INT15 to enable the delayed tranmitter interrupt routine. End INT13 conditionally, that is, if M0.0 is set and you are using a PC/PPI cable. M0.0 1 VB1 15 11 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 37 Enable Transmitter Timer and Interrupt, Transmit the Data Load memory bit M0.0. If memory bit M0.0 is on (has a signal state of 1), attach interrupt event 10 to INT1 to enable the 5-ms time-out timer for the transmitter. Attach interrupt event 9 (Port 0: Transmit complete) to INT10 to enable the transmitter interrupt. Transmit by means of Port 0 the data buffer (TABLE) that starts at variable memory byte VB600 (the first byte of the Transmit buffer; that is, transmit the message). End INT13 conditionally, that is, if M0.0 is set. M0.0 1 10 10 9 VB600 0 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 38 If a Parity Error Occurs, Enable the Quiet Line Timer and Receiver If there is a parity error, load special memory bit SM0.0 to process this network every scan cycle. Attach interrupt event 10 to INT0 to enable the 5-ms quiet line timer. Attach interrupt event 8 (Port 0: Receive character) to INT14. When a character is received at Port 0, control is transferred to INT14 to enable the quiet line receiver. SM0.0 0 10 14 8 Network 39 End of Interrupt Routine INT13 End INT13. Network 40 Interrupt Routine INT14 Start INT14 to enable the time-out interrupt. 14 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 41 Retrigger the 5-ms Quiet Line Time-Out Timer Load special memory bit SM0.0 to process this network every scan cycle. Attach interrupt event 10 to INT0 to retrigger the 5-ms quiet line timer. SM0.0 0 10 Network 42 End of Interrupt Routine INT14 End INT14. Network 43 Interrupt Routine INT15 Start INT15 to enable the delayed transmitter interrupt. This routine provides a delay between the last character that is received and the first character that is transmitted. The PC/PPI cable requires a two-character delay time and some modems also require a delay. 15 PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD. INDUSTRIAL AUTOMATION Network 44 Delayed Transmitter Load special memory bit SM0.0 to process this network every scan cycle. Detach interrupt event 11 from all interrupt routines to disable the transmitter interrupt. Attach interrupt event 10 to INT1 to enable the 5-ms time-out timer for the transmitter. Attach interrupt event 9 (Port 0: Transmit complete) to INT10 to enable the transmitter interrupt. Transmit by means of Port 0 the data buffer (TABLE) that starts at variable memory byte VB600 (the first byte of the Transmit buffer; that is, transmit the message). SM0.0 11 1 10 10 9 VB600 0 Network 45 End of Interrupt Routine INT15 End INT15. PROLIFIC SYSTEM AND TECHNOLOGY PVT.LTD.