Intelligent Eight-Channel Communications Controller
—
CD1865
Datasheet
71
7.2.7
Sending Breaks
Line breaks may be sent by embedding the following sequences in the data stream (all values are
given in Hex):
00 81
break condition and stay there until one of the following conditions is met:
Send Break:
Enter line-break condition for at least one character time. The line enters the
1. Another character needs to be sent.
2. If the Insert Delay Special Character Sequence immediately follows the Send Break Sequence,
the duration of the break transmission is extended by the amount of the programmed delay.
The Insert Delay Sequence is: 00 82 xx. This inserts a delay of
‘
xx
’
(interpreted as an unsigned
binary number) times the programmed timer
‘
tick
’
set by the Prescaler Period registers.
Multiple insert delay commands can be executed consecutively by the CD1865 to allow delays
of arbitrarily long length. If
‘
xx
’
is a zero, no delay is inserted.
3. The Stop Break Sequence
‘
00 83
’
is encountered next. This sequence is optional, and exists to
provide a way to terminate a break without actually sending another character. If another
character is being sent anyway, no Stop Break is required.
If there is no more data to be sent, the TxD pin remains in the state it was left in by the last
character. Since the Stop bit is always a
‘
1
’
, the line is left in the idle state after any character,
except for the break character. The break character leaves the line in the
‘
0
’
state until more data
needs to be sent. Long breaks can be sent by simply sending one break and then waiting. To
terminate the break, send the Stop Break Sequence or send another character.
Sending long breaks has precedence over the Send Special Character Command, for example, the
time delay duration must pass before the special character is sent.
7.2.8
Sending Inter-Character Delays
In some applications it is desirable to pause between characters. For example, certain types of
electro-mechanical teletype equipment cannot handle characters continuously at their specified bit
rate. To accommodate this, the CD1865 allows insertion of a delay between characters.
The user embeds an escape sequence into the Output Data Stream to generate delays between
characters. When the CD1865 encounters the Insert Delay Escape Sequence, it sets the Transmit
Timer to the value contained in the Escape Sequence. When the timer expires, the CD1865 loads
the next character into the Transmit Shift register and resumes output (unless the next character
begins another Escape Sequence). The Escape Sequence for an inserted delay consists of three
characters:
‘
00
’
,
‘
82
’
, and
‘
tt
’
. The time-out value
‘
tt
’
is expressed in timer ticks.
7.2.9
Summary of Special Transmitter Commands
The ETC bit in COR2 must be set to enable the following functions:
Char. Sequence
Effect
00 00
Send one-null character