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12.5.9 Internal registers - read and write operations
The SSI module is provided with a universal register interface that enables access to up to 64 regis-
ters.
These are accessed via the process data. For write access, it must be ensured beforehand that the
register write interface is in the default status and that a write access operation is therefore not cur-
rently active. This is ensured if REG_WR = 0 in the process output data, and is confirmed in the pro-
cess input data with REG_WR_AKN = 0. Write access is then possible. The following values must be
transferred with the process output data for this:
REG_WR_ADR = register address,
REG_WR_DATA = value to be written (32 bit)
REG_WR = 1 (write command)
The SSI module acknowledges the processing of the write command via the process input data by
signaling REG_WR_AKN = 1. REG_WR_ACEPT = 1 in the process input data confirms whether the
write operation to the register was successfully completed. If the register could not be written (no
access authorization, out of value range,...), this is indicated by REG_WR_ACEPT = 0. The write oper-
ation must then be terminated by REG_WR = 0 in order to resume the default state.
The address specified at REG_RD_ADR of the process output data is used for read access. The read
register content is entered in REG_RD_DATA (bytes 4-7) if the address at REG_RD_ADR was
accepted in the process input data and if REG_RD_ABORT = 0 confirms that the register was read
error-free. REG_RD_ABORT = 1 indicates that the register could not be read. REG_RD_ADR in the
process input data then contains the address that could not be accessed successfully. The user data
is then set to ZERO.
Register access and meaning
Designation No. Description Default (HEX)
REG_SSI_POS 0 Actual binary SSI encoder value
REG_MAGIC_NO 1 Magic number (0xaa55cc33)
REG_HW_VER 2 Hardware version
REG_SW_VER 3 Software version
REG_SF 4 Special Function register
5…13 reserved
REG_WR_ADR 14 Pointer register OUT
REG_RD_ADR 15 Pointer register IN
REG_DIAG1 16 Diagnostics
17…19 reserved
REG_PARA1 20 parameter data 0×1901 0000
21…31 reserved
REG_GRAY_POS 32 Actual Gray-coded SSI encoder
value.
REG_SSI_FRAME 33 Complete frame read from SSI
encoder.
REG_CMP1 34 Reference value 1 0×0000 0000
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