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2.8.2
Data Transfer Methods
The 4863 transfers data between the GPIB bus and the 48 digital I/O lines
with byte I/O commands, by bit manipulation, with data string commands,
or by transparent data strings. The 2363 does not have transparent data
transfer capability.
Commands transfer data as a parameter in the command. Byte oriented data
commands like PORTn directly address and transfer data to or from an
unconfigured port on the digital interface. Each port command transfers
eight bits of data. Bit manipulation commands let the user set and reset bits
in an unconfigured output byte or read a bit in an unconfigured input byte.
Data polarity can be on a bit basis.
String oriented data commands like PORT? and VALUE pass multiple
bytes of data per command to one or more ports that have been configured
as inputs or outputs. Transparent data transfer passes the same data strings
used with string commands without the command syntax by addressing the
interface at a second address. Data polarity and format is the same for all
of the bytes assigned to a string.
Characters in a data string can be HEX characters, user assigned ASCII
characters, ASCII numbers or binary characters. When HEX or user
assigned ASCII characters are used, each character represents a four bit
BCD or HEX value on four of the digital I/O lines. It takes two HEX
characters to program or to read a eight bit byte. HEX code is the sixteen
characters 0 thru 9 and A thru F for a value of 0 to 15. The TALK format
provides a TABLE entry command where the user can assign his own
sixteen characters. The LISTEN format provides a 4833 selection with an
alternate input character set of 0-9 and :;<=> ? are used for compatibility
with ICS's earlier Model 4833 Parallel Interface. Listen string transfers
from the GPIB bus or serial ports must end with a linefeed character with
or without EOI asserted. The 4863 appends a linefeed character with EOI
asserted to the input data when talking on the GPIB bus or a carriage return
for serial transmissions.
e.g. The HEX characters 3E sets eight output bits to 0011 1110
ASCII numbers transfers an eight bit pattern on the digital I/O connector as
a decimal value that is the sum of the binary bit weights for all of the bits
set to logic 1. Value is 0 to 255. Values for multiple bytes are separated by
commas.
