This module holds keys to a Tymnet circuit {SIK, SOK and CCK} and provides keys {described below} with modified function. This module is responsible for handling certain idiosyncrasies of ASCII terminals and echoing. It handles any delays required by the terminal, simulates tab and formfeed if necessary and compensates for the finite width of the terminal paper {does linefolding}. {For the purpose of linefolding, it may want to turn off echoing by the remote if the user is inputting near the right margin.} See (p2,newtcem) for new TCEM's.

It may optimize output, for example by suppressing output of carriage return when the carriage is already at the left margin, suppressing output of non-printing characters, or converting output spaces to tabs.

SIK2

This key obeys the SIK3 protocol except that screen mode is not supported. Characters from SIK (the circuit) are assumed to be ASCII. They are checked for parity if desired and masked to 7 bits. Control codes are checked for validity and either consumed or encoded in the byte stream as bytes with values greater than 127.

Data passing through SIK2 is broken up into transmissions as described above. The data in each transmission is echoed promptly according to the echo mask.

Control codes {(cc)} that get delivered to the SIK2 user always cause activation and never are echoed. The following control codes can appear:

orange/gray/black balls, break

A zapper from the circuit (EOF on SIK) causes the TCEM to destroy itself, which in turn signals EOF on SIK2. If the consumer signals EOF, it is ignored.

{nonref}Implementation note:

Some implementations, in order to take advantage of Tymnet remote echoing, may cause to be echoed characters which should not be echoed. This may happen even though the echo mask is not changed.

These implementations may remember the characters which were echoed in error. If the next characters output match the characters echoed in error (as if the SIK2 user had decided to echo the characters itself after all), those characters are deleted from the output stream, since they have already been printed.

Input is not impeded due to backpressure on the output. There is a buffer of characters to be echoed and this buffer may overflow.

This key is a byte stream consumer. Bytes with value less than 128 are assumed to be ASCII characters and are sent to SOK (the circuit) after being processed as described above. Other bytes are control codes:
yellow ball, gobbler {(cc)}

A zapper from the circuit (EOF on SOK) causes the TCEM to destroy itself, which in turn signals EOF on SOK2. If the producer signals EOF, communication is ended but the TCEM is not destroyed.

Sending a gobbler does not affect the state of echoing or tab stops. It may cause terminal characteristics to not be set, and may gobble a hang character. It does gobble echoes.

128 yellow ball

129 orange ball

130 gobbler

131 break

134 gray ball

135 black ball

Like the standard CCK3 function (cck3) except:

CCK2(0 ...) is not yet implemented.

CCK2(1 ...) is not yet implemented.

CCK2(2;==>;) "Send zapper"

Works regardless of backpressure.

CCK2(4;==>0;SIK,SOK,CCK) "Destroy TCEM"
Destroys the TCEM. EOF is signalled on SIK2 and SOK2.

If SIK2 is consuming, SIK is returned, otherwise DK(0) is returned in this position.

SOK is returned if it is available, otherwise DK(0) is returned in this position. There is no way to determine whether SOK will be available.

Since no limit for SOK is returned, the user will have to assume a limit of zero initially.

Programming note: See the tap operations on the CCK key for reacquiring full use of the circuit after the destruction of the TCEM.

Design Note: Perhaps we should have a "wait for SOK and then destroy TCEM" command. This might not be prompt if output were blocked down stream.

CCK2(14 ...) is not yet implemented.

CCK2(kt;==>X'40E';)

TCEMK(0,(1,tc);==>c,(1,val);) returns the value of terminal characteristic number tc in val.
C = 2 if tc is invalid, 0 otherwise. Val=255 if the value is unknown.

For some characteristics there is a delay after setting a value before the new value is sensed. This delay can be arbitrarily long while SIK2 is consuming.

TCEMK(1,(1,tc),(1,val);==>c;) sets the value of terminal characteristic number tc to val.
C = 2 if tc or val is invalid, 0 otherwise.

The terminal characteristics and their numbers are:
0 Input baud rate
See the Tymnet Interface Guide.

1 Output baud rate
See the Tymnet Interface Guide.

2 Input parity
Value 0 means the high order bit of characters from the terminal is not significant.

Value 1 means the terminal is expected to send even parity as the high order bit.

3 Output parity
Value 0 means the terminal ignores the high order bit of characters.

Value 1 means the terminal expects even parity.

4 Parameter A
See the Tymnet Interface Guide.

5 Parameter B
See the Tymnet Interface Guide.

6 Parameter C
See the Tymnet Interface Guide.

7 Parameter D
See the Tymnet Interface Guide.

8 X-enable
See the Tymnet Interface Guide.

9 Reverse X-enable
See the Tymnet Interface Guide.

10 "Half Duplex"
Value 0 means the terminal does not echo input, value 1 means it always does.

11 CR Delay
See the Tymnet Interface Guide.

12 Linesize
The number of characters that may appear on a line. 0 < linesize < 256.

13 Tab Switch
Value 0 means the terminal doesn't print tab.

Value 1 means the terminal can print tab, but the tab stops can't be set from the computer.

Value 2 means the terminal can print tab and can set tabs on command from the computer. LOOSE END How?

14 Backspace Switch
Value 0 means the terminal doesn't print backspace, 1 means it does.

15 Formfeed Switch
Value 0 means the terminal doesn't obey formfeed, 1 means it does.

TCEMK(2;==>;) sends a hang character.

TCEMK(kt;==>X'1030E';)