Multitech MMH900 User Manual page 66

keep up with the volume of data sent to it. There are
two types of flow control available on the MultiMux.
The software based Xon/Xoff and hardware based
Clear to Send (CTS). F0 turns flow control off, F1
selects CTS flow control, and F2 selects Xon/Xoff
flow control. The way channel devices control the
data flow to them from the MultiMux is called Pacing
(see Pacing command).The combination of Flow
Control for regulating data from individual channel
devices and pacing for regulating data to individual
channel devices is how data transfers are regulated
so that no data is lost.
F3-F4 ENQ/ACK Flow Control
These two commands control the selection of a
special flow control system used in Hewlett Packard
computer systems. It is sometimes referred to as
Enquire/Acknowledge flow control because it's
based on the computer sending an inquiry (ENQ)
and then expecting an acknowledgment (ACK). F3
turns on this feature and F4 turns off the feature.
F5-F6 Pacing Control
The Pacing Control command (F5-on, F6-off) is the
means used to control data flow to channel devices.
Pacing is necessary when devices operating on a
mux channel require more than one character time
to process the data, the pacing commands initiate
control so that data is not lost in the transfer
process. The MultiMux is shipped with pacing off
and it will have to be turned On if your channel
device cannot accommodate the data volume.The
pacing method used is determined by the type of
flow control.
F7-F8 Pass EIA Signals
The Pass EIA Signal commands (F7-on, F8-off) are
the commands that enable or disable individual
MUX INITIATED
FLOW CONTROL
DATA
Channel
Mux
Device
Flow control stops the
input of data to the mux
Chapter 5 - Commands
CHANNEL DEVICE
INITIATED PACING
DATA
Channel
Mux
Device
Pacing stops the output
of data from the mux
66