BECKHOFF EtherCAT Technology Section I - Manual (Page 91)

EtherCAT State Machine
Slave Controller – Technology I-71
10.1 EtherCAT State Machine Registers
The state machine is controlled and monitored via registers within the ESC. The master requests state
changes by writing to the AL Control register. The slave indicates its state in the AL Status register
and puts error codes into the AL Status Code register.
Table 35: Registers for the EtherCAT State Machine
Register Address Name Description
0x0120:0x0121 AL Control Requested state by the master
0x0130:0x0131 AL Status AL Status of the slave application
0x0134:0x0135 AL Status Code Error codes from the slave application
0x0141[0] ESC Configuration Device emulation configuration
NOTE: The PDI Control register is set via SII EEPROM/IP Core configuration, other registers might not be
available in specific ESCs. Refer to Section II and Section III for details.
10.1.1 AL Control and AL Status Register
Writing the AL Control register (0x0120:0x0121) initiates a state transition of the device state machine.
The AL Status register (0x0130:0x0131) reflects the current state of the slave.
Table 36: AL Control and AL Status Register Values
Register [3:0] AL Control Register 0x0120 AL Status Register 0x0130
1 Request Init state Init state
3 Request Bootstrap state (optional) Bootstrap state (optional)
2 Request Pre-Operational state Pre-Operational state
4 Request SAFE-Operational state SAFE-Operational state
8 Request Operational state Operational state
10.1.2 Device Emulation
Simple devices (without µController) have the device emulation enabled (0x0141[0]=1). The AL
Control register is directly copied into the AL Status register by the ESC. The master should not set
the Error Indication Acknowledge bit for such slaves at all, because setting this bit would result in
setting the Error Indication bit
– although no error occurred.
10.1.3 Error Indication and AL Status Code Register
The slave indicates errors during a state transition by setting the Error Indication flag (0x0130[4]=1)
and writing an error description into the AL Status Code register (0x0134:0x0135). The master
acknowledges the Error Indication flag of the slave by setting the Error Indication Acknowledge flag
(0x0120[4]).
For more information on defined AL Status Codes, refer to the EtherCAT Knowledge Base available at
the EtherCAT Technology Group website (
http://www.ethercat.org , Guidelines and Protocol
Enhancements).