iL Series User Manual
California Instruments
Rev B
17
Pin
Input/Output
Description
1
Output
Reserved for service use
2
Input
Receive Data (RxD)
3
Output
Transmit Data (TxD)
4
Output
Data Terminal Ready (DTR)
5
Signal ground
6
Input
Data Set Ready (DSR)
7
no connection
8
no connection
9
Output
Reserved for service use
Table 8 : RS232C DB-9 connector pin assignments
DB-9 PC
DB-9 AC Source
Pin
1
2
3
4
5
6
7
8
9
Pin
1
2
3
4
5
6
7
8
9
Direction
output
input
output
output
-
input
-
-
output
Description
reserved
Receive data(RxD)
Transmit data (TxD)
Data Terminal Ready (DTR)
Signal Ground
Data Set Ready (DSR)
no connect
no connect
reserved
Figure 9 RS232C PC to AC Source cable wiring diagram
Hardware Handshake
The RS-232C interface uses the DTR (data terminal ready) line as a holdoff signal to
the bus controller. When DTR is true, the bus controller may send data to the power
source. When DTR goes false, the bus controller must stop sending data within 10
characters, and must not send any more data until DTR goes true again. The power
source sets DTR false under two conditions:
1. When the input buffer is full (approximately 100 characters have been received),
it will set DTR false. When enough characters have been removed to make
space in the input buffer, DTR will be set to true, unless condition 2 (see below)
prevents this.
2. When the power source wants to "talk", which means that it has processed a
query, and has seen a <newline> message terminator, it will set DTR false. This
implies that once a query has been sent to the power source, the bus controller
should read the response before attempting to send more data. It also means
that a <newline> must terminate the command string. After the response has
been output, the power source will set DTR true again, unless condition 1 (see
above) prevents this.
The power source monitors the DSR (data set ready) line to determine when the bus
controller is ready to accept data. It checks this line before each character is sent,
and the output is suspended if DSR is false. When DSR goes true, transmission will
resume. The power source will leave DTR false while output is suspended. A form
of deadlock exists until the bus controller asserts DSR true to allow the power source
to complete the transmission.
Summary of Contents for iL Series
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