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Buffer Addresses for Displays
Buffer address
is a term used to identify a location in the device buffer corresponding
to a position on the display screen. The buffer addresses begin with 0 for row 1,
column 1. The maximum buffer addresses are as follows:
Address
1919
2559
3439
3563
Row, Column
24, 80
32,80
40, 80
27, 132
Model Emulation
Model 2
Model 3
Model 4
Model 5
12/14
Bit Addressing
Host Data
In the data stream sent from the host to the 3708, the buffer address is transferred
using a 2-byte field. This field may be coded using either 12- or 14-bit buffer
addressing. In the data stream sent from the 3708 to the host, the buffer address is
transferred using a 2-byte field, but only 12-bit buffer addressing is used.
In data from the host, the first 2 bits of the first address byte determine whether 12-
or 14-bit addressing is used. These bits have the following values:
00
01
10
11
14-bit binary address follows
12-bit coded address follows
Reserved
12-bit coded address follows.
When the flag bits are 00, the next 14 bits are a buffer address in binary form. The
14 bits consist of the remainder of the current byte (6 bits) and 8 bits of the next
byte. No address translation is necessary.
When the flag bits are 01 or 11, a 12-bit address is indicated. This is created from
the remaining 6 bits of the first byte, concatenating them to the last 6 bits of the
second byte.
When the flag bits are 10, a negative response of X' 1005' is sent back to the host,
and the write operation is terminated.
3270 Data Stream Commands
Commands are sent from the host application to the 3708 to initiate the total or
partial writing, reading, or erasing of data in the 3708 device buffer. (For
information about buffer addressing see "Converting Between ASCII and EBCDIC"
on page F-l.) The following table shows the commands that the 3708 accepts, the
abbreviation for that command, and the EBCDIC code for the command.
EBCDIC
Command
Abbreviation
Code
Write
W
X'Fl'
Erase All Unprotected
EAU
X'6F'
Erase/Write
EW
X'F5'
Erase/Write Alternate
EWA
X'7E'
Read Buffer
RB
X'F2'
Read Modified
RM
X'F6'
Read Modified All
RMA
X'6E'
4-4
IBM 3708 Description
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