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Set Buffer Address Register and Start Command
This four-byte command initiates display regen-
eration for the selected 2250.
It
is normally used
after, and can be chained to, a Write Buffer, Read
Buffer, Read Cursor, Insert Cursor, and Remove
Cursor command. The second two bytes of this
command specify the buffer location at which re-
generation should start:
Buffer Addresr
0
7
8
15
Any even buffer address from 0 through 32, 766
can be specified.
The first two bytes of this command cause re-
generation of all attached displays to stop and
cause a request for two bytes (a buffer address)
from the channel. These bytes, when received at
the interface control section, are passed to the
address register for the selected 2250. The com-
mand then enables display regeneration for the
selected 2250 by allowing two bytes to be read from
the buffer; the first byte is from the location ad-
dressed by the command, and the second byte is
from the next consecutive location. These should
be the first two bytes of an order, initiating re-
generation operations in the 2840 and the 2250.
Regeneration of the other attached displays then
continues automatically.
The buffer starting location selected by this
command should always have an even-numbered
address and should always contain the first (SM)
byte of an order. If both conditions are not met,
sequential buffer locations are read and decoded
in the buffer register until an SM byte is decoded
from an even address; at this time, the byte in the
next sequential address is read and decoded, start-
ing the regeneration operation.
Programming Note: The Set Buffer Address
Register and Start command resets Graphic or
Character mode,
if
active, in the selected 2250.
Set Buffer Address Register and Stop Command
This command can be used to stop regeneration for
a selected 2250. It causes regeneration to stop,
if
in progress, and initiates a request to the channel
for two buffer address bytes. When received from
the channel, these two bytes are placed, via the
interface control section and the buffer register
(Figure 13) , into the address register for the
selected 2250. The address bytes are coded as
shown for the Set Buffer Address Register and
Start command. The Set Buffer Address Register
and Stop command will usually precede Write,
Read, Insert Cursor, or Remove Cursor com-
mands and may be chained to commands that speci-
fy these operations.
Set Audible Alarm Command
This immediate command causes activation, for
a short period, of a buzzer (single-stroke audible
alarm) at the selected 2250.
Programming Note: Bit 34 of the Set Audible
Alarm CCW (the Suppress Incorrect Length Indi-
cator bit) should be a
1.
Set Programmed Function Indicators Command
This command is used to light and extinguish pro-
grammed function keyboard indicators as specified
in four data bytes that follow the command byte.
These indicators, numbered 0 to 31 (Figure 12),
are associated with the four data bytes as follows:
Byte
Bit Position
0
1
2
3
4
5
6
7
0
0
1
2
3
4
5
6
7
1
8
9
10
11
12
13
14
15
2
16
17
18
19
20
21
22
23
3
24
25
26
27
28
29
30
31
An indicator will be on (lit) when its associated
data bit is a 1; it will be off
if
its associated data
bit is a 0. The operation of this command does not
affect regeneration.
Insert Cursor Command
This immediate command must be preceded by a
Set Buffer Address Register and Stop command
which stops regeneration for the selected 2250 , if
in progress, and identifies the buffer location to
which the cursor is to be assigned. The cursor in-
dication for the addressed buffer location is then
set without disturbing the data byte in that location.
If a Set Buffer Address Register and Stop command
is not issued before the Insert Cursor command
when the buffer is operating, the Insert Cursor
command is rejected, the Unit Check bit is set in
the status byte, and the Command Reject and Buf-
fer Running bits are set in the sense byte. Once
inserted, the cursor can be repositioned with alpha-
meric keyboard action, with a Set Buffer Address
Register and stop command followed either by a
Remove Cursor command or an Insert Cursor com-
mand, or with a Set Buffer Address and Stop com-
mand and an Insert Cursor command followed by
a Write Buffer command (replacing the character
at the cursor position) and an Insert Cursor com-
mand.
( 2840 Operations with the Channel
37
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