BECKHOFF ET1100 - Manual (Page 90)

PDI description
III-76 Slave Controller – ET1100 Hardware Description
6.5.4 µController connection using Byte Select signals (BSn)
In case the µController does not provide Byte High Enable, and Byte Select signals (BS2, and BS3 for
32 bit µController) are available, they can be used to distinguish between 8 and 16 bit accesses. The
signal BS3 (active low) is equivalent to ADR[0], and BS2 (active low) is equivalent to BHE (active low).
For Byte Select mode the Byte access mode configuration bit has to be set to zero (BHE or Byte
Select mode).
Table 73: Byte Select vs. A[0] and BHE
µController EtherCAT device Access
ADR[0] nBS3 nBS2 ADR[0] BHE
(act. low)
0 0 0 0 0 16 bit access (low and high byte)
0 0 1 0 1 8 bit access (low byte, even address)
1 1 0 1 0 8 bit access (high byte, odd address)
1 1 1 1 1 invalid access