Sensoray 7429 - Manual (Page 15)

PROGRAMMING
C OMMUNICATION
Programming of the 7429 is achieved via a set of built-in commands which the 7429's
onboard microcomputer is programmed to recognize. These commands are sent from
the host processor to the 7429.
Some commands produce responses from the 7429; these responses are sent from 7429
to the host processor. The following sections describe the mechanism by which this bi-
directional communication operates.
Programming Model
The coprocessor occupies two contiguous I/O ports in the STDbus I/O space. Both
ports may be written to and read from, but each port has a distinctly different function
for read and write operations.
Programming model
The base port (7429 board low port address) is the data port between 7429 and host pro-
cessors. Commands are sent to the 7429 and command responses are passed back to
the host through this port.
Physically, the data port consists of two hardware registers: command and data. When
the host sends a command to the coprocessor, it is really storing a byte in the command
register. When fetching a command response from the 7429, the host is reading a byte
from the data register. Because the command register is write-only and the data register
read-only, they can share the same port address.
The status port (7429 board high port address) may be read by the host to obtain copro-
cessor status information. This status information is discussed in the next section.
When the host writes a byte into the status register, a hardware reset is invoked on the
7429. This can be useful during system software development. Data written to the sta-
tus register is ignored.
Status Register
The status port provides the host with four status bits for monitoring various aspects of
sensor coprocessor status. When the host inputs a byte from the status port, a byte of
the following form is returned:
I/O AD DRESS F UNCT ION READ WRIT E BASE ADDRESS + 0
BASE ADDRESS + 1
DAT A REGI ST ER COM MA ND REGIST ER
STAT US REGIST ER BOARD RESET