User's Manual

Turbo PMAC User Manual
44 Talking to Turbo PMAC
* Don’t care, not used
** System dependent setting
Delta Tau’s software packages for the PC, such as the Executive and Setup programs, and the PComm32
communications library, do not support VME bus communications, because there is no standard VME
communications method under the Microsoft Windows operating systems, even for PC-compatible VME-
bus computers.
Wire Buses
Recently, high-speed wire links have become cost-effective and widespread enough to provide an
economical but high-bandwidth link between host computer and controller. Delta Tau presently supports
two of these links: USB and Ethernet. These links essentially match the speed of backplane buses for the
transfer of large data sets in either direction, but are only about half as fast in response time to short
commands, due to added delays from the processors at each end of the link.
USB
Several Turbo PMAC configurations support the use of Universal Serial Bus (USB) communications.
Initial implementations used 12Mbit/sec USB1.1 links; newer implementations use the 480Mbit/sec
USB2.0 links. Remember that USB1.1 devices can be used on 100 Mbit/sec buses.
Ethernet
Several Turbo PMAC configurations support the use of Ethernet communications. Initial
implementations used 10Mbit/sec Ethernet links; there are plans to upgrade to 100Mbit/sec. Remember
that 10Mbit/sec devices can be used on 100Mbit/sec networks.
Both TCP/IP and UDP/IP protocols are supported. The simpler UDP/IP protocol is strongly
recommended, as it is more efficient, and the additional packet information and handshaking
acknowledgments of TCP/IP are not required for the point-to-point communications used here. Use of
the TCP/IP protocol with a computer running a Microsoft Windows operating system is particularly
inefficient, due to an operating system time-out on every command/response event.
Dual-Ported RAM
The bus communications ports, both backplane and wire, provide optional support for communications
through a shared-memory interface using dual-ported RAM. ASCII text commands can be issued through
the DPRAM, but the main virtue of DPRAM is its binary data structures that permit direct parallel access
to many pieces of data.
These structures include data-reporting buffers, in which Turbo PMAC repeatedly updates fixed registers
in DPRAM with commonly desired position information, such as motor positions; data gathering buffers,
permitting the real-time uploading of synchronously gathered data; background variable data copying
buffers, which permit the repeated copying to and from user-specified Turbo PMAC registers; binary
rotary motion-program download buffers for the fastest possible downloading of motion program files;
and user-defined structures.
For the ISA and VME buses, Turbo PMAC variables I93 and I94 set the address of the DPRAM on the
bus at power-up/reset. For the PCI bus, the host computer’s operating system sets this address
automatically. For the wire buses, the DPRAM does not directly map into the host computer’s memory
space; software routines such as Delta Tau’s PComm32 library create a virtual image of the DPRAM in
the host computer’s memory, making the remoteness of the DPRAM transparent to the applications
program.
Several communications structures in DPRAM can individually be enabled with I-variables:
• DPRAM ASCII Communications: I58 and I56
• DPRAM Motor Data Foreground Reporting: I48 and I47
• DPRAM Motor Data Background Reporting: I57 and I50