User's Manual

PMAC Dual-Ported RAM User Manual
Dual-Ported RAM Communications 1
DUAL-PORTED RAM COMMUNICATIONS
PMAC’s Option 2 provides an 8K x 16 bit dual-ported RAM that allows PMAC and its host to share an
area of fast memory. For the PMAC PC and the PMAC Lite, Option 2 is a separate board that sits on the
PC bus and cables to PMAC. For the PMAC VME, Option 2(V) consists of ICs added to the main board
itself. Option 2 is not available for the PMAC STD. For all versions of the PMAC2, Option 2 consists of
ICs added to the main board itself. The dual-ported RAM can be used for extremely fast communication
of data and commands to and from PMAC.
Uses of DPRAM
The typical use in writing to PMAC is for a very fast repetitive downloading of position data and/or rotary
program information in real time. The typical use in reading from PMAC is getting very fast status
information repetitively. PMAC supports both automatic functions for the DPRAM communications, and
user-designated functions.
Data such as motor status, position, velocity, following error, etc. can be continuously updated and written
to DPRAM by PLC programs or automatically by PMAC. Without using DPRAM, this data must be
accessed by sending PMAC on-line commands, such as ?, P, V, and F, through the VME mailbox registers
or over the PC bus. This same data may be obtained much faster via the DPRAM without the time
required to send the command through the communications port and wait for the response.
For non-automatic uses, PMAC usually accesses the dual-ported RAM through M-variables that are
addressed to these locations. This can work for reading or writing. The M-variable formats likely to be
used are X:, Y: (for 1 to 16 bits), DP: (for 32-bit fixed point), and F: (32-bit floating point). For sending
data back to the host, PMAC's data gathering function can also be used, directed to the dual-ported RAM
rather than the regular RAM (I45 controls). See the Analysis Features section of the PMAC manual for
details.
Setting up the PC Bus Dual-Ported RAM (Option 2)
There is no hardware setup or connections for the Option 2 DPRAM on the PMAC2-PC or PMAC2-Lite.
It is factory installed on the PMAC2 itself. For the PMAC PC bus cards, the DPRAM card plugs into an
available PC-slot to the right side of your PMAC PC or Lite card. The PMAC and DPRAM card together
occupy 2 PC slots. The two short cables provided connect the DPRAM to the CPU on the PMAC. The
50-pin cable connects P3 of DPRAM to J2 of PMAC (piggy-back board) or J9 of PMAC Lite. The 10-pin
cable connects P4 of DPRAM to J4 of PMAC (piggy-back board) or J10 of PMAC Lite.