Siemens 6SE2101-1AA01, Руководство по эксплуатации

Страница: 44 / 110

English 7/9

Siemens plc 1993
7.5 USS Serial Communications Protocol
As for the simple protocol described in section 7.4, the USS protocol transmits bytes as sequences of 11 bits (1
start bit, 8 data bits, 1 parity bit and 1 stop bit).
USS messages consist of 14 bytes, organised as follows:
STX LGE Device
Number
PKE
high
low
IND
high low
PWE
high low
PZD1
high low
PZD2
high low
BCC
0 1 2 3 4 5 6 7 8 9 10 11 12 13
STX is the ASCII character value 02.
LGE is the net data length. This is fixed by the 6SE21 at 12 (0C hex) bytes.
Device Number is as set by parameter P21.
PKE is a word used for parameterisation control.
IND is an array index word. It is not used on the 6SE21. Reply messages always have this set to 0.
PWE is a word used to transfer parameter values and error codes.
PZD1 is the control/status word. It transfers commands to the inverter and status information to the controller.
PZD2 is the main set–point. This is used to request output frequency from the inverter and will return actual output
frequency / actual output current values.
BCC is the Block Check Code, formed by exclusive ORing the previous 13 bytes together.
A two character delay is imposed between receipt of the command message at the inverter and its reply. The total
delay time between receipt of a command and the first byte of the reply will vary between approximately 2.5 ms and
17.5 ms at 9600 baud.
7.5.1 Using the USS Protocol
The inverter may be in one of the following states when controlled via a USS serial link:
NO CONTROL Inverter will not respond to serial commands
AUTOMATION CONTROL Inverter is able to respond to serial commands
SWITCH ON INHIBIT Inverter will respond to commands except RUN
RUNNING Inverter is active and running
STOPPED Inverter is active but stopped
TRIPPED Inverter is in SWITCH ON INHIBIT and awaiting a trip acknowledge
The 6SE21 is always in the USS ‘ready’ and ‘ready to run’ states.
7.5.1.1 Enabling the Serial Link
When the USS link is first established (parameter P20 set to 003), the inverter is in the USS SWITCH ON INHIBIT
state. The inverter will not respond to run/jog commands until this state has been cleared.
To clear this state, an OFF1 command must be transmitted, with AUTOMATION CONTROL (bit 10 PZD1) set to 1.
To send an OFF1, set PZD1 bits 0 to 3 = ‘1 1 1 0’.
SWITCH ON INHIBIT status is indicated in the reply message by PZD1 bit 6 being set to 1.
A suitable value of PZD1 to initialise the serial link is 047E hex.