Document No. 232OTTL0812 - pg. 1/2
Four-Channel Optically Isolated
RS-232 to TTL Converter
Model 232OTTL
Description
The 232OTTL is an RS-232 to TTL converter with 1500V isolation. Channels TD and RTS convert RS-232
to 0-5V TTL signals and channels RD and CTS convert 0-5V TTL signals to RS-232. The RS-232 side has a
DB25 female connector pinned out to plug directly into the COM port of a computer or any other DTE device. The
TTL side has a DB25 male connector.
Signal Lines
The 232OTTL supports 4 signal lines and ground as shown in Figure 1. Two of these four lines, TD and
RTS, convert RS-232 inputs to TTL outputs. The other two lines, RD and CTS, convert TTL inputs to RS-232
outputs. These lines communicate at baud rates up to 38.4 kbps.
Figure 1: Signal Lines
RS-232
TTL
DB25 female
DB25 male
DCE
TD
2 9
RD
3 14
RTS
18
4
CTS
5 23
GND
7
7
It is important that only TTL logic (0 to +5V) is used for the TTL side of the converter. The maximum
sinking current for one TTL output is 8 mA. The maximum source current for one TTL is 0.8 mA. Signal levels
are inverted by the converter in its standard configuration as shown in Table 1. See the section titled Options
Requiring Modification if non-inverted outputs are desired.
Table 1: Standard Inverted Outputs
TTL Input RS-232 Output TTL Output RS-232 Input
high (>2.0V) -5V maximum, -9V typical high (>2.0V) -5V maximum, -9V typical
low (<0.8V) +5V minimum, +9V typical low (<0.8V) +5V minimum, +9V typical
Power
The RS-232 side of the 232OTTL derives its power from the outputs of the host RS-232 port. TD, RTS,
and DTR lines may be used to port power the RS-232 side. A minimum of two of these lines in either high or low
states is required for proper operation. If your port meets the low voltage requirements of RS-562, you will need to
externally power the RS-232 side of the 232OTTL. An RS-562 port, typically found on handheld computers, will
only produce about 3.7 volts, which is not adequate to power the isolator. To externally power the RS-232 side,
connect the positive lead of the +12VDC power supply to pin 25 and the GND lead to pin 12 of the DB25 female
connector.
The TTL side of the 232OTTL requires a power supply to operate. +12VDC may be connected to the
power jack on the side of the unit, or on pins 25 (+12VDC) and 12(GND) of the DB25 male connector. See the
section titled Options Requiring Modification if it is necessary to power the TTL side from a +5V supply.
Options Requiring Modification
The 232OTTL may be modified to non-inverted signals as shown in Table 2 by placing a jumper wire across JP1:A
labeled NI.
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International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax 433-5104
European Office: Westlink Commercial Park Oranmore Co. Galway Ireland +353 91 792444 Fax +353 91 792445
PRODUCT INFORMATION B&B ELECTRONICS
Document No. 232OTTL0812 - pg. 2/2
Table 2: Modified to Non-Inverted Outputs
TTL Input RS-232 Output TTL Output RS-232 Input
high (>2.0V) +5V minimum, +9V typical high (>2.0V) +5V minimum, +9V typical
low (<0.8V) -5V maximum, -9V typical low (<0.8V) -5V maximum, -9V typical
The 232OTTL may also be modified to accept a +5V supply on the TTL side. Remove the 0 ohm surface mount
resistor labeled R13 and place a jumper wire across JP1:B labeled +5V. A +4.75 to +5.25V at a maximum of
25mA is necessary to power the TTL side of the converter when this modification is made.
For assistance with these modifications, or to have the 232OTTL modified before shipment, call B&B Electronics.
Specifications
Signals: 4 channels, TD, RD, RTS, CTS
RS-232 side pinned out as DCE
TTL/CMOS compatible voltage levels (low < 0.8V, high > 2.0V)
Inverted outputs (non-inverted available with modification)
38.4 kbps maximum
Power
RS-232 Side: Port-powered by TD, DTR, and RTS (requires two lines in any state)
Or +12 to 16 VDC at 30 mA maximum on pins 25 and 12
TTL Side: +12 to 16 VDC at 25 mA maximum on power jack or pins 25 and 12
(+5 VDC available with modification)
Dimensions: 3.1 x 2.1 x 0.8 in (7.8 x 5.4 x 2.1 cm)
Environment: 0 to 70C
www.bb-elec.com orders@bb-elec.com support@bb-elec.com
International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax 433-5104
European Office: Westlink Commercial Park Oranmore Co. Galway Ireland +353 91 792444 Fax +353 91 792445
PRODUCT INFORMATION B&B ELECTRONICS