Introduction; Possible Conversions - Black Box CMA005A Manual

USER PROGRAMMABLE CAP
The User Programmable CAP lets two incompatible
devices that use RS-232 interfaces communicate
with each other. The unit is programmed for your
application through internal DIP switches and
jumpers. The unit's 32K of RAM can be allocated in
different amounts for each port.
Below is a list of optional equipment you can use to
integrate the unit into your application. See
Appendix A for the pinouts of the listed cables.
• Card Rack
• Power Supply
• Cables:
CAP-to DTE Cable
CAP-to-Modem Cable
CAP to AT ® Cable
Straight 9-Pin Cable
CAP-to-PC Cable

2.1 Possible Conversions

The User Programmable CAP can convert between
two devices for any of the following parameters:
• Word Structure — Defines the structure of the
asynchronous characters transmitted and
received over the RS-232C interface. The User
Programmable CAP's communication ports can
be set individually for your devices' word
structure.
Word Structure Options:
a) 5, 6, 7, or 8 Data Bits
b) Even, Odd, Mark, Space, or No Parity Bit
c) 1, 1.5, or 2 Stop Bits
• Buffer Flow Control — The Programmable CAP
provides the protocol for stopping and starting
data transfer between two devices.
Buffer Flow Control Options:
1. Hardware Flow Control — A pin of the
RS-232 interface in used for buffer flow
control. If the pin being monitored by the
sending device is +12 V, the device can
transmit data. If the pin is -12 V, the device
cannot transmit data. A device attached to
4

2.0 Introduction

the User Programmable CAP is asked to
stop transmitting when only 256 bytes of
unused space remain in the buffer. The
unit permits the device to transmit again
when only 256 bytes of information
remain in the buffer. The unit is DTE; it
sources DTR and monitors CTS.
2. ENQ/ACK Flow Control — Some devices
request permission to transmit a block of
asynchronous data by sending an "ENQ"
control code (05H). The device transmits
the block only if it receives an "ACK"
control code (06H) in response. A block
may be anywhere from 1 to 256 bytes. If a
larger block size is required, you will have
to do custom programming.
NOTE
The User Programmable CAP will not
initiate ENQ for ENQ/ACK protocol; it
only responds with ACK to an ENQ. In
some applications, custom firmware
can be configured to have the User
Programmable CAP initiate ENQ.
3. X-ON/X-OFF Flow Control — The
sending device is allowed to transmit data
until it receives an "X-OFF" control
character (13H). After it receives this
character, it must wait until it receives an
"X-ON" control character (11H) before it
can transmit again. The device attached
to the Programmable CAP is asked to
stop transmitting when only 256 bytes of
unused space remains in the buffer. The
Programmable CAP permits the device to
transmit again when the buffer is emptied
to a point where only 256 bytes of
information remain.
4. No Flow Control — For those situations in
which a device uses no flow control, the
Programmable CAP can be configured to
always receive and transmit data without
any protocol.
• Baud Rate — A unit of signaling speed equal to
the number of signal events per second. The
Programmable CAP 's communication port's
baud rate must be set to match that of the