⟦19bd17a2e⟧

RcTekst


╱04002d4e0a0006000000000201413140000000000000000000000000000000000000000000000000050f19232d37414b555f69737d8791ff04╱
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┆b0┆┆a2┆┆e2┆┆a1┆TABLE OF CONTENTS ┆05┆PAGE↲
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┆b0┆1.  INTRODUCTION ┆f0┆............................................   1↲
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┆b0┆2.  PROTOCOL┆f0┆ ................................................   2↲
    2.1  Address Character ..................................   3↲
    2.2  Data Character .....................................   3↲
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┆b0┆3.  SELECTION OF CIRCUIT II┆f0┆ .................................   4↲
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┆b0┆4.  HARDWARE AND EXAMPLES┆f0┆ ...................................   5↲
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┆14┆┆b3┆                                ┆0b┆↲
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┆b0┆┆a1┆1.       INTRODUCTION↲
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         ┆84┆The protocol is designed as a local network for VDU ↓
┆19┆┆89┆┄┄terminals in the RC850 family and are connected to an ↓
┆19┆┆89┆┄┄RC3900.↲
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         ┆84┆The line used is a high speed twisted pair connection ↓
┆19┆┆89┆┄┄with the following characteristics:↲
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         - Half duplex operation↲
         - High speed serial data transfer↲
         - A line length of maximum 1500 meters.↲
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         ┆84┆The data format used is a polled character by character ↓
┆19┆┆89┆┄┄format, which allows transfer of any 8 bit data.↲
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         ┆84┆The address character allows for multipoint operation, ↓
┆19┆┆89┆┄┄with a maximum of 32 connected terminals.↲
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┆b0┆┆a1┆2.       PROTOCOL↲
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         ┆84┆The CIRCUIT II is used as a local network between an ↓
┆19┆┆89┆┄┄RC3900 (master) and the work stations RC850 (terminals).↲
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         ┆84┆The terminals are controlled by a poll from the master. ↓
┆19┆┆89┆┄┄A poll can have two different forms:↲
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         1) a poll without data from the master↲
         2) a poll with data from the master↲
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         ┆84┆In both cases the terminal has to answer the poll, this ↓
┆19┆┆89┆┄┄can again be in two different forms:↲
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         1) an answer without data from the terminal↲
         2) an answer with data from the terminal↲
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         ┆84┆A bit on CIRCUIT II has a length of 4 usec. If it is a ↓
┆19┆┆89┆┄┄logic one all 4 usec. are at same level. If it is a ↓
┆19┆┆89┆┄┄logic zero the bit will be 2 usec. at one level and then ↓
┆19┆┆89┆┄┄2 usec. at the other level. The start sequence from the ↓
┆19┆┆89┆┄┄master consist of two 6 usec. bits,  without level ↓
┆19┆┆89┆┄┄shift. From the terminal the start sequence consists of ↓
┆19┆┆89┆┄┄two one and one zero bit. The signals on CIRCUIT II have ↓
┆19┆┆89┆┄┄no defined polarity. Bits are detected by a shift in ↓
┆19┆┆89┆┄┄levels. See fig. 1.↲
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         Figure 1: CIRCUIT II bits, and start sequences.↲
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         ┆84┆A character from the master consists of 12 bits:↲
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         ┆84┆The start sequence (two bits), 8 databit, a paritybit, ↓
┆19┆┆89┆┄┄and a stopbit.↲
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         ┆84┆A character from the terminal consists of either 4 or 14 ↓
┆19┆┆89┆┄┄bits:↲
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         ┆84┆If the terminal does not have data to send, the 4 bits ↓
┆19┆┆89┆┄┄are sent. They are 4 ones. This is done while the master ↓
┆19┆┆89┆┄┄otherwise will wait time out thereby delaying the ↓
┆19┆┆89┆┄┄overall transmission speed.↲
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┆8c┆┆83┆┆c0┆↓
         ┆84┆The 14 bits are sent when there is data. They are the ↓
┆19┆┆89┆┄┄start sequence (three bits), 8 databit, a parity bit and ↓
┆19┆┆89┆┄┄two stop bit.↲
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┆b0┆┆a1┆2.1      Address Character↲
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         ┆84┆A poll is always started by an address character which, ↓
┆19┆┆89┆┄┄when demodulated will have the following form: ↲
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         bit     ┆a1┆1   2   3   4   5   6   7   8   9↲
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         value   A   A   A   A   A   X   C   X   P↲
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         ┆84┆The first 5 bits are the address bits and are labelled ↓
┆19┆┆89┆┄┄A. This gives a maximum of 32 terminals. The X's are ↓
┆19┆┆89┆┄┄don't cares. C is the bit that tells if data is ↓
┆19┆┆89┆┄┄following. A logic 1 indicates that data is following, a ↓
┆19┆┆89┆┄┄logic 0 that no data is following. P is the parity bit.↲
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┆b0┆┆a1┆2.2      Data Character↲
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         ┆84┆The data characters have the following form:↲
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         bit    ┆a1┆1   2   3   4   5   6   7   8   9↲
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         value  D   D   D   D   D   D   D   D   P↲
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         ┆84┆As it can be seen there are 8 data bits and one parity ↓
┆19┆┆89┆┄┄bit.↲
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         ┆84┆If there is no data for the master, the character sent ↓
┆19┆┆89┆┄┄will be 4 ones. No start bit or parity bit.↲
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┆b0┆┆a1┆3.       SELECTION OF CIRCUIT II↲
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         ┆84┆The terminal is used as a TTY. Therefore the user has to ↓
┆19┆┆89┆┄┄choose between LINE 1 and CIRCUIT II. This is done by ↓
┆19┆┆89┆┄┄means of the two V24 signals labelled DTRA and RTSA.↲
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         ┆84┆Line 1 is selected by activating DTRA for a minimum of ↓
┆19┆┆89┆┄┄25 nsec before RTSA. CIRCUIT II is selected activating ↓
┆19┆┆89┆┄┄RTSA for a minimum of 20 nsec before DTRA.↲
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         ┆84┆Each time DTRA is activated the selection circuit is ↓
┆19┆┆89┆┄┄triggered. Changes in the RTSA have no effect. Every ↓
┆19┆┆89┆┄┄time CIRCUIT II is selected, an address to the selection ↓
┆19┆┆89┆┄┄circuit must be sent. This is done by sending a ↓
┆19┆┆89┆┄┄character from the MIC board to the CTA501 which will be ↓
┆19┆┆89┆┄┄an 8 bit data byte with the address in the 5 lower bits, ↓
┆19┆┆89┆┄┄and with odd parity. The address is the secondary ↓
┆19┆┆89┆┄┄address in the terminal and changeable in CONFI.↲
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         ┆84┆Normal communication between the CTA501 and the MIC ↓
┆19┆┆89┆┄┄board is with 9600 baud, 1 startbit, 8 databits, even ↓
┆19┆┆89┆┄┄parity and 1 stopbit.↲
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┆b0┆┆a1┆4.       HARDWARE AND EXAMPLES↲
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         ┆84┆Cable type       :    2x2x0.6mm (e.g. NEK PT/CN-1)↲
         Cable length     :    maximum 1500 meters↲
         Wall receptacle  :    TF669 (WRF501)↲
         Terminal cable   :    TF673 (KBL604)↲
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         ┆84┆As shown in fig. 1, the connections to the receptacles ↓
┆19┆┆89┆┄┄must not be made as stubs. The cable has to be wired ↓
┆19┆┆89┆┄┄through the receptacle.↲
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         Figure 1: Installation of DUAL CIRCUIT↲
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         ┆84┆↲
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┆1a┆┆1a┆nual RCSL↲
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⟦19bd17a2e⟧ RcTekst

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