three signals to TTL levels and transfers them to
the first (XC5210) of two large field
programmable gate arrays (FPGAs) on the
daughter board. Inside this device the data is
de-serialised and transferred to COM port 5 of
DSP 1.
A second FPGA (XC5206) is used to generate
stimulus pulses. There are four similar
programmable timing blocks within the device.
Two are used to control the EMG stimulators and
two for the EP stimulator. Software running on the
DSP sets the parameters for these according to
what the user requires. A watchdog timer is also
implemented in this FPGA. If the DSP software
does not re-trigger the watchdog every 127 ms
then the stimulus timer output pulses are inhibited.
This prevents out-of-control stimulation if the
system crashes.
A quad RS232 interface is also provided on the
daughter board. These four interfaces are used to
provide control and status information for the
EMG stimulators, the head-box and the control
panel. The interfaces are implemented using a
Texas Instruments TL16C554 quad UART and a
LT1134 RS232 level converter.
A digital to analogue converter (DAC) and audio
amplifier are provided so that the EMG signals can
be heard. DSP software is responsible for writing
the audio data samples into a 512 deep FIFO. The
data is then clocked out of the FIFO into the DAC
by control logic in the XC5206 FPGA. The
amplifier uses a pair of TDA2030 devices in
bridge mode. Power MOSFET switches allow the
selection of an internal or external loudspeaker in
Synergy Portable. However there is no internal
speaker option in the Synergy Mobile. Note that
because the amplifier is operated in bridge
mode neither of the outputs should be shorted
to ground.
Additional logic in the FPGAs provide a
programmable interrupt controller, an interface to
the EP stimulator (if fitted), auxiliary trigger inputs
and stimulus outputs, and an input for a patient
response button.
A PAL device is used to provide the address
decode, loudspeaker selection and FPGA
programming signals.
4.3 The Control Panel & Electrical
Stimulators.
A schematic diagram for this unit is shown in
Figure 4.3. This schematic diagram includes the
optional internal stim which can be built into the
Control panel.
Control functions
A micro-controller is used to monitor all control
panel operations. Communication between the
controller and the mainframe is made serially by
an RS-232 link.
Control panel rotary and push-button switches, and
external footswitches routed to the control panel
are all decoded by the micro-controller which then
transmits this information to the PC tower via the
connection box.
On units with dual external electrical stimulators,
the front panel stimulus intensity and duration
controls do not function.
The micro-controller also drives the “Acquire” and
“Stim” LED’s on the control panel at the
appropriate times.
The board is supplied with +12V, which is
regulated to +5V for the on-board devices.
Electrical Stimulator functions
The internal electrical stimulator and the external
stimulator probe have almost identical circuits, and
therefore this overview will cover both.
An oscillator circuit drives the primary of an
isolating transformer, with a sync. signal from the
mainframe ensuring that the stimulator isolated
supply remains synchronised with the amplifier
system.
The output from the isolating transformer is
rectified and regulated to supply the d.c. supplies
for the isolated side of the circuitry. A switching
regulator and pump circuit generate a +350V
supply for the stimulator output circuit which is
only enabled when in an EMG stimulating mode.
Control of the stimulator is via an RS-232 link
through opto-isolators to a programmed PIC. The
PIC sets up the stimulus driver circuits, by
controlling the output of a dual DAC – one output
for voltage, one output for current.
The direction of the stimulus pulse is selected by a
positive or negative trigger signal from the DSP
Daughter board. The trigger pulse for the required
polarity signal is input to the primary of an
isolating transformer, and the output turns on the
appropriate pair of FET switches to connect the
Issue A May 1998
TECHNICAL OVERVIEW
Chapter 4 Page 4
Synergy Mobile Workshop Manual