11
KRAMER ELECTRONICS LTD.
7.3
RS-232 Communication Protocol for SD-7308
RS-232 communication with the SD-7308 is defined using a one byte protocol as defined below. The physical
interface with the controller should be via a null-modem connection.
MSB
LSB
0
N7 N6 N5 N4 N3 N2 N0
7
6 5 4 3 2 1 0
0
Machine No. 1
New Switch Status
N7
is only used for communication between the slave and the master and is always 0 for communication with
the PC.
N6N5N4
is the binary value of the machine we are addressing minus one, e.g., if we wish to address the master
(machine 1 by definition), then N6N5N4 = 000, if we wish to address machine 6, then N6N5N4 = 101.
N3N2N1N0
is the binary value of the input to be selected, e.g. N3N2N1N0 = 0111 is equivalent to pressing
switch 7 on the front of the machine.
Several special codes are also valid:
N3N2N1N0
= 1101 requests that the machine being addressed sends its present status to the PC, i.e. which
input is selected on that machine.
N3N2N1N0
= 1100 requests that the machine being addressed sends its "lock status" to the PC, i.e. whether the
machine has locked onto the incoming video or not. If locked, the machine replies with the code N3N2N1N0 =
1011, if not locked, N3N2N1N0 = 1010.
When data is sent to the switcher in order to change its status, (i.e. to route a new input to the output), the
machine replies by returning that same byte of information.
The switching protocol is "bi-directional", i.e. if a button was pressed on a front panel, the byte of information
sent from the master to the PC is as described above.
The data transfer rate is selected via Dipswitch 7: 1200 baud if Dipswitch 7 is in the OFF position (factory
default), or 9600 baud if Dipswitch 7 is in the ON position. There is no parity, 8 data bits and 1 stop bit.
7.4
DIPSWITCH settings for the SD-7308
Up to 8 machines may be controlled using a single RS-232 port by setting the first machine as the "master," and
the others as "slaves". The machines are then daisy-chained using a 9-pin flat-cable, and connected to the PC
via the null-modem adapter.
The dipswitches are to be set as follows (table shows setting for 1200 baud. For 9600 baud, set switch 7 to
ON):
Switch Setting
Machine
Number
1 2 3 4 5 6 7 8
1 (Master)
OFF OFF OFF OFF OFF ON OFF ON
2 ON OFF OFF OFF OFF OFF OFF OFF
3 OFF ON OFF OFF OFF OFF OFF OFF
4 ON ON OFF OFF OFF OFF OFF OFF
5 OFF OFF ON OFF OFF OFF OFF OFF
6 ON OFF ON OFF OFF OFF OFF OFF
7 OFF ON ON OFF OFF OFF OFF OFF
8 ON ON ON OFF OFF OFF OFF OFF
Table 4: DIPSWITCH settings for the SD-7308