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NOTES ON THE INTERFACE TO THE USART
CONNECTIONS TO THE USART
SETTING UP THE USART
PROGRAMMING THE USART
North Star HSIO-4
APPENDIX B
The USART data sheet describes all possible
USART connections. Not all of these
connections, however, are supported by the
HSIO-4. Specifically, the SYNDET pin can be
used only as an output with the HSIO-4. It
cannot be used as an input to initiate HUNT
mode. When HUNT mode is required, it must be
set by the appropriate command instruction.
The RESET signal for the USART is derived from
the S-100 POC/ line, and is asserted when the
computer is powered up or when the computer is
restarted with the reset switch. If a RESET is
required at any other time, the USART can be
internally reset with the appropriate software
instructions. (Refer to the USART data sheet
for specific command instructions.)
It is necessary to pause between resetting a
USART and issuing the set up commands. This is
is a problem only if ports are reset and set
up one at a time. This problem can be avoided,
and the necessary pause provided, by resetting
the USART for ports 1, 2, 3, and 4 in sequence
and then setting up each USART in similar
sequence. To achieve the required delay when
setting up only one port, execute two XTHL
instructions after issuing the RESET command.
The following sequence of command words will
accomplish a soft reset and ready an
individual USART for a mode instruction.
Output
3
to USART Status Control address
Output
3
to USART Status Control address
Output 64
to USART Status Control address
After programming the USART with mode and
command words, the USART data should be read to
remove any extraneous character.
75
User/Technical Manual
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