Configuration Switches; Rts/Cts Delay - Bell 5902 Hardware Manual

4.5

Configuration Switches

The 5902 modem has 16 configuration switches. They specify the modem communication
parameters and operating modes. See Figure 1: 5902 Module Layout for switch locations. The
functions are described in detail below.
The switches can be changed with the power applied. All changes take effect immediately.

To CLOSE a switch, press down on the right side of the switch.

To OPEN a switch, press down on the left side of the switch.
CAUTION: Do not use a pencil, mechanical pencil or pen to adjust the switches. Graphite and
ink can cause switch failure. A paper clip is a good tool for adjusting switches.
4.5.1

RTS/CTS Delay

The CS0 and CS1 switches control the RTS/CTS delay. There are four options. The delays are
longer when the RCD option is enabled, as radios usually require longer delays.
DELAY (RCD open)
DELAY (RCD closed)
CS0 switch
CS1 switch
The RTS and CTS signals coordinate data transmission between the modem and the DTE. When
RTS is asserted by the DTE, the modem turns on its carrier, keys the radio and starts a delay. At the
conclusion of the delay, CTS is asserted by the modem to allow the DTE to transmit data. This delay
has different functions according to the modem duplex setting.
4.5.1.1 Half Duplex (FDX open)
The RTS/CTS delay allows the modem carrier to be transmitted to and be detected by the receiving
modem or modems. The receiving modem requires time to detect and synchronize to the carrier,
before it can accept data. Radios may take some time to key up to full power before transmitting.
Radio repeaters also require time to engage. The RTS/CTS delay provides this time.
When RTS is asserted by the DTE, the 5902 modem closes the KEY output, turns on the transmit
carrier, and starts the delay. When the delay has expired, the modem asserts CTS to allow the DTE
to transmit.
The modem will not transmit carrier or start the RTS/CTS delay, while carrier is being received,
unless constant carrier operation is selected (refer to section 4.5.3-Carrier Loss Delay). This
prevents the modem from transmitting at the same time as another modem.
4.5.1.2 Full Duplex (FDX closed)
The RTS/CTS delay has no effect on modem operation in full duplex mode. The modem always
transmits a carrier.
The RTS/CTS delay is functional and can be used to insert a pause between transmissions. To use
this feature, the DTE device must use RTS/CTS handshaking (half duplex operation). When the
DTE is ready to transmit data, it asserts RTS and waits for CTS to be asserted by the modem. When
CTS is asserted, the DTE transmits the data. The DTE releases RTS at the end of transmission. This
causes a pause before each transmission.
5902 Bell 202 Modem Hardware Manual
October 19, 2007
25 ms 50 ms
67 ms 133 ms
open closed
open open
125 ms 250 ms
266 ms 1000 ms
open closed
closed closed
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