Stanford Research Systems SIM918 Operating And Service Manual page 23

1.6 SIM Interface
CAUTION
1.6.2.1 Direct interface cabling
note about grounds
SIM918 Precision Current Preamplifier
on Pin 2 for a low-going TTL-compatible output indicating a status
message. See Section 3.5 for the description of status messages.
The SIM918 has no internal protection against reverse polarity, missing
supply, or overvoltage on the 5 V and the 15 V power-supply pins. Sup-
ply voltages above 5 5 V on Pin 13, above 16 V on Pin 14, or below 16 V
on Pin 7 are likely to damage the instrument. SRS recommends using the
SIM918 together with the SIM900 Mainframe for most applications.
If the user intends to directly wire the SIM918 independent of the
SIM900 Mainframe, communication is usually possible by directly
connecting the appropriate interface lines from the SIM918 DB–15
plug to the RS–232 serial port of a personal computer.
from the SIM918 directly to RxD on the PC, TXD directly to TxD. In
other words, a null-modem-style cable is not needed.
To interface directly to the DB–9 male (DTE) RS–232 port typically
found on contemporary personal computers, a cable must be made
with a female DB–15 socket to mate with the SIM918, and a female
DB–9 socket to mate with the PC's serial port. Separate leads from
the DB–15 need to go to the power supply, making what is sometimes
know as a "hydra" cable. The pin connections are given in Table 1.3.
DB–15 F to SIM918
10
11
7
13
14
1
8
9
Table 1.3: SIM918 direct interface cable pin assignments.
The distinct Signal Ground and Power Ground, and the chassis
ground, are not directly connected within the SIM918. The power
4
Although the serial interface lines on the DB–15 do not satisfy the minimum
voltage levels of the RS–232 standard, these lines are typically compatible with
desktop personal computers.
Name
DB–9 F
3 TxD
2 RxD
5 Computer Ground
to Power Supply
15 V DC
5 V DC
15 V DC
Signal Ground (separate wire to Ground)
Power Ground (separate wire to Ground)
Chassis Ground (separate wire to Ground)
1 – 11
4
Connect RXD