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3
GENERAL ARCHITECTURE OF VM-USB AND ITS USER INTERFACE
Note: The information is this section is relevant only for VM_USB controllers with firmware
950000405 or later. If you have an earlier version consider updating or see Appendix C.
Most of the VM_USB registers take the form of a VME address within the VM_USB and
can be communicated with by using VME calls to the appropriate VME address. These
registers are part of the Internal register file. The registers that cannot be communicated with
in this way are in Table 1.
Table 1. Internal VM)USB registers that aren't seen as VME space
PA
1
4
-
-
3.1 Action Register (Address = 1 / 0x1)
12-15
-
The action register is a special-purpose write-only register controlling the mode of operation
of VM-USB and the generation of internal trigger/reset signals. By its design, it can often be
accessed when other VM-USB actions are under way and, most notably, when VM-USB is
placed in autonomous data acquisition mode.
Bit 0 of the Action Register controls the operating mode of VM-USB and distinguishes
between the interactive and autonomous data acquisition modes. In the interactive mode,
VME commands (individual or a sequence) are performed directly in response to a USB
packet received from the host, while in the data acquisition mode, sequences of VME
commands are executed, pursuant to lists stored in a dedicated VM-USB memory block. Any
of the configurable 8 lists (stacks) is executed upon the receipt of the associated trigger
signal, which may be a signal at the user NIM input I1, detection of a valid VME IRQ, or a
USB trigger of scaler readout. When bit 0 of the Action Register is set, VM-USB is in data
acquisition mode; otherwise it is in interactive mode.
Bit 1 of the Action Register is a write-only bit, such that writing "1" to it generates an
internal signal of 150ns duration, called USB Trigger. This signal can be routed to user NIM
outputs O1 or O2, used as an input to multiplexed internal user devices of VM-USB (such as
delay and gate generators and scalers), and/or displayed on user LEDs.
Bit 2 of the Action Register is a write-only bit, such that writing "1" to it, clears a number of
internal registers. It is intended primarily for use during firmware debugging.
WIENER, Plein & Baus GmbH
Device
Action Register (AR)
VME Command Generator (VCG)
VME Commmand Stacks
Common Output Buffer
8-11
5-7
-
-
scaler dump SYSRES
4
3
clear
14
2
1
USB trigger
Start/stop
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0
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