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9.5
Pulse Modulation in the SPC 4-2
The SPC 4-2 has circuits for a direct connection SIM1-optocoupler-SPC 4-2
(PROFIBUS PA attachment) using the current-saving interface of the SIM 1. A
separate adapter circuit is no longer necessary.
The circuit is designed for a single application:
PROFIBUS-PA
Operating frequency on SPC 4-2: 2 MHz
Baud rate: 31.25 kbauds
Description
The frames received from SIM1 are not passed on to the SPC 4-2 in their original
form. To save current, the SIM converts the frame to a series of short pulses. It
therefore appears at the SPC 4-2 in the following form:
Each rising edge in the frame produces a high pulse with a width of 5µs, each
falling edge a high pulse with a width of 2µs: between pulses, the signal is level 0.
The original frame is recovered in the receive unit.
When a frame is sent by the SPC 4-2 , this pulse train is generated from the frame
to be sent. The only difference is the inverted polarity: To activate the optocoupler,
low pulses must be generated instead of high pulses.
Activation:
To start the pulse modulation the user must set the pulse modulation bit in mode
register 3 (address 31BH).
Pulse modulation (bit 0):
following reset).
122
0:
pulse modulation is deactivated (status
1:
Pulse modulation is enabled.
PROFIBUS Controller SPC 4®-2 LF
C79000-G8976-C157-3
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