VIASYS Bear Cub 750PSV, Service Manual, Page: 84 / 98

84
Bear Cub 750PSV
Alternatively, the ventilator can be interfaced to a DTE device with the following "null-
modem" interface. (See table 9-2).
Table 9-2: Alternate Pin Assignment
DTE Name DTE Pin Direction DTE Pin DTE NAME
GND 5 - - - - - - - - - - 5 GND
RxD 2 <<- - - - - - - - 3 TXD
TxD 3 - - - - - - - ->> 2 RXD
RTS 7 - - - - - - - ->> 1 DCD
DTR 4 - - - - - - - ->> 6 & 8 DSR & CTS
RI 9 Not used 9 RI
Software Protocol
The ventilator’s RS-232 port has two modes of communication. The first mode
continuously outputs real time data every 10 msec and will provide non-real time
data upon request from an external device. This mode requires 19.2 kBaud data
rate. This second mode will only provide non-real time data upon request from an
external device (all other data rates). The mode of communication is selected by the
user upon installation simultaneously with and as a function of the baud rate.
Continuous Output (Default Mode)
The continuous output mode communicates at 19.2 kBaud and sends out the real
time data (flow, pressure, breath phase, breath type, and alarm status) every 10
msec. Upon request, non-real time data will also be sent, however it may delay the
real time data by up to 25 msec. Note, the real time data is queued by the ventilator
so that it is only delayed and not lost.
Data Upon Request
All non-real time data, consisting of control settings, alarm settings and status, and
monitor values will be provided upon request from an external device. This data can
be requested at any transmitted baud rate. The buffer for requested data will be
limited, but will have the capability such that at least three (3) transactions (requests)
can be handled (queued) at a time. Any additional data requests prior to completion
of a corresponding number of message transmissions may be ignored by the
ventilator.
Data Format
The messages are sent and received in variable length data packets. All packets are
preceded by a SYN character, and terminated by a check sum.
The purpose of the SYN character is to enable the receiver to detect the start of a
message, therefore it is an illegal character within a data packet. If the binary value
L2346 Revision B June 2004