Electronic Systems Technology ESTEEM192S Wireless Modem User Manual PART 5

Electronic Systems Technology Wireless Modem PART 5

USER MANUAL PART 5

CHAPTER 5RS-232C/422/485 INTERFACINGDTE VS DCEFLOW CONTROLMEMORY BUFFERSDATA TERMINAL READYRS-422/485 CONFIGURATIONRS-232/422/485 PORT PINOUT TABLE
CHAPTER 5RS-232C/422/485 INTERFACINGRevised: 11 Feb 99 5-2 DTE vs. DCEThe ESTeem is configured as a Data CommunicationEquipment (DCE) device. The following signals areavailable at the RS-232C connector located at the front ofthe unit. Pin Description---------------------------------------------------------------------1 FG Shield Ground2 TXD Transmit Data (Input)3 RXD Receive Data (Output)DCE 4 RTS Request To Send (Input)5 CTS Clear to Send (Output)7 SG Signal Ground8 DCD Data Carrier Detect (Output) 12 RTS Request To Send (Output) 20 DTR Data Terminal Ready (Input) 22 Ring Ring Indicator (Output)The important thing to remember is that for the ESTeem tocommunicate with an external device, the data output frompin 3 of the ESTeem RS-232C connector must be connectedto the data input of the device you are connected to;otherwise, the ESTeem won't work. Likewise, the datainput to pin 2 of the ESTeem must be connected to the dataoutput of the device you are connected to. Normally, if theequipment you are connecting to looks like a terminal orcomputer (DTE), its input, Receive Data (RXD), will be onpin 3 its output, Transmit Data (TXD), will be on pin 2. Therefore, the ESTeem can be connected directly. If the device you are connecting to is configured as amodem (DCE), its output will be on pin 3. If thisconfiguration is connected to the ESTeem, damage mayresult to the ESTeem or the connecting device. In this case,you can purchase a null connector that internally reversespins 2 and 3. Whatever your situation may be, it is always best to checkthe manual on your particular device and connectaccordingly.Purchase or fabricate a RS-232C shielded cable for yourESTeem. The ESTeem requires a standard male 25 pin Dconnector on one end of the cable for proper connection. Remember to install the small retaining screws on eitherside of the cable connector. Tightening these screws keepsyou from accidentally losing connection with your ESTeem.Notes: • The ESTeem requires a shielded RS-232 cable. This isto prevent unwanted electrical noise from entering theESTeem and also to prevent any electrical noise fromgetting out of the ESTeem. • Remember -- always use a shielded RS-232C cable.• Pins 9, 10, 14, & 16 are used for RS-422/485interfacing and should be left open if not used.FLOW CONTROLThe ESTeem can be enabled to support SOFTWARE orHARDWARE flow control. Software Flow ControlSoftware flow control is enabled by the XSFLOW (on/off)command in the ESTeem. When XSFLOW is ON theESTeem will respond to <XOFF>, (stop) and <XON>, (off)commands from the RS-232 port. The factory defaultsetting is ON. The default value for START is 17 (CTRLQ) and for STOP is 19 (CTRL S).Hardware Flow ControlHardware flow control is enabled by the XHFLOW (on/off)command in the ESTeem. The factory default value isOFF.When XHFLOW is enabled (on) the control signal lines,Request To Send (RTS, pin 4), Data Carrier Detect (DCD,pin 8), and Clear To Send (CTS, pin 5) are available to theuser at the RS-232C connector. The CTS and RTS signalsare used to control the flow of data into and out of theESTeem. The CTS signal on pin 5 is used to control the data into theESTeem. When CTS is set (high on pin 5) the modem isready to receive data. When CTS is reset (low on pin 5) theESTeem is not ready to receive data. The RTS signal is used to control data out of theESTeem. RTS is set (high on pin 4), by the user to indicateto the ESTeem that the user is ready to receive data. Whenreset, the user is not ready to receive data. Note: Low = On, High = Off.MEMORY BUFFERSThe ESTeem has a 4000 byte buffer on the TRANSMITSIDE (outgoing data) and a 4000 byte buffer on theRECEIVE SIDE (incoming data).
CHAPTER 5RS-232C/422/485 INTERFACINGRevised: 11 Feb 99 5-3 Transmit BufferThe outgoing data buffer will hold two data blocks beforethe ESTeem will enable its RS-232C hardware/softwareflow control on data coming into the modem if the networkis busy. A data block in this example is a block of data thatis defined by the PACKLENGTH or SENDPAC characterwhich ever occurs first.Therefore, if PACKLENGTH = 10 the modem will input amaximum of 20 bytes before it enables itshardware/software handshake line (two 10 byte packets). Inanother example, if PACKLENGTH = 2000 but the datablock is terminated by the SENDPAC character before theinput buffer reaches the full 2000 bytes, the buffer will stillhold only two data blocks if the network is busy.In order to utilize the 2000 bytes storage for small datapackets (bar code readers, etc.), program the modem usingthe following guidelines:PACKLENGTH = 2000 SENDPAC = 255TERMC = ON TERMT = 10Note: Set the TERMT time greater than the pausebetween data bursts.By programming the above parameters the ESTeem willbuffer the incoming data packets and automatically transmitthe data when the 2000 byte buffer is filled or the TERMTtime limit is met. This will allow the customer to use twoblocks of 2000 or 4000 bytes before the modem enables therespect hardware/software control.Receive BufferIf the device that the receiving ESTeem is outputting datato, enables its respective hardware or software control, themodem will store 4000 bytes of data before flow controllingoff the transmitting ESTeem.DATA TERMINAL READY (DTR)A software switch, DTR_ENAB (ON/OFF) is provided inthe ESTeem for monitoring the status of a device connectedto pin 20 of the RS-232C connector. The factory defaultsetting is OFF. When this command is enabled the ESTeemwill monitor the DTR signal on pin 20. If the DTR linebeing supplied to the ESTeem, from the user, is at a SPACE(high) condition then the ESTeem is enabled. If the DTRline is at a MARK (low) condition then the ESTeem isdisabled.This signal is normally used by the ESTeem modem as anindication that connection is made to a device that is on lineand ready to transmit/receive data.RS-422/485 CONFIGURATIONThe ESTeem will support the requirements of the EIAStandard RS-422/485. This is a four (4) wire interfaceconsisting of the TRANSMIT DATA (-), TRANSMITDATA (+), RECEIVE DATA (-), AND RECEIVE DATA(+). These signals are available at the 25 pin RS-232Cconnector on the modem.Pin Description 9 BTR (-) TRANSMIT DATA (-)10 BTR (+) TRANSMIT DATA (+)DCE 14 BRX (+) RECEIVE DATA (+)16 BRX (-) RECEIVE DATA (-)This interface is designed to provide unipolar differentialdrive to twisted pair or parallel wire transmission lines.Note: The ESTeem can be factory configured for 2-wireRS-485 interfacing. Call EST Customer Supporton 509-735-9092.
CHAPTER 5RS-232C/422/485 INTERFACINGRevised: 11 Feb 99 5-4 Refer to Chapter 1 “Starting Out” to set the ESTeem RS-232 data rate. ESTeem RS-232C/422/485Port Pin-Out TablePin No. Function1Shield Ground2Transmit Data (TxD)3Receive Data (RxD)4Request To Send (RTS Input)5Clear To Send (CTS)6Data Set Ready (DSR)7Signal Ground8Data Carrier Detect (DCD)19 Mode Control20 Data Terminal Ready (DTR)22 Ring Indicator (RI)12 Request To Send (RTS Output)9RS-422/485 Transmit Data (-)10 RS-422/485 Transmit Data (+)14 RS-422/485 Receive Data (+)16 RS-422/485 Receive Data (-)

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