Serial Interface Module Circuitry
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Serial Interface Module Circuitry
Each Serial Interface Module has a 60-pin connector that provides all
signal and power connections to the MVME761 transition module.
TTL-level signals
All TTL-level signals, with the exception of data and clocks, are active
low. The pullup resistors on the MVME761 transition module drive all
TTL inputs to the SIM to a known logic level.
SIMs
The SIMs have surge suppression circuitry for all port signals going to the
external connector. This consists of a series resistor and a dual 15V clamp
diode to chassis ground. All series resistors are 100 ohms except on the
EIA-530 balanced drives, which use 10 ohm series resistors.
❏
EIA-232-D SIMs employ MC145406 ICs as line transmitters to
convert the TTL output signals from the MVME260x, MVME270x,
MVME360x, or MVME460x module to EIA-232-D voltage levels.
As line receivers, the MC145406 ICs convert the EIA-232-D input
signals to TTL voltage levels which are sent to the VME module.
The MC145406 transceiver IC requires a series diode on the +12V
supply and a clamp diode to logic ground on the -12V supply. The
diodes are located on the transition module rather than on the SIM
due to space limitations.
❏
EIA-530 and X.21 SIMs employ AM26C31CD ICs as transmitters
to convert the TTL output signals from the MVME260x,
MVME270x, MVME360x, or MVME460x module to balanced
signals. As line receivers, the AM26C32CD ICs convert the
balanced input signals to TTL signals which are sent to the VME
module.
❏
V.35 SIMs employ LTC1345T ICs as transmitters to convert the
TTL output signals from the MVME260x, MVME270x,
MVME360x, or MVME460x module to balanced signals. As line
receivers, the LTC1345R ICs convert the balanced input signals to
TTL signals which are sent to the VME module.
