2.8.4. APB-AP Control/Status Word Register, CSW, 0x00

The APB-AP Control/Status Word Register is used to configure and control transfers through the APB interface. Figure 2.22 shows the bit assignments.

Figure 2.22. APB-AP Control/Status Word Register bit assignments

Table 2.29 shows the bit assignments.

Table 2.29. APB Control/Status Word Register bit assignments


Software access enable.

Drives PDBGSWEN to enable or disable software access to the Debug APB bus in the APB multiplexor.

b1 = Enable software access

b0 = Disable software access.

Reset value = b0. On exit from reset, defaults to b1 to enable software access.

[30:12]--Reserved SBZ.

Specifies the mode of operation.

b0000 = Normal download/upload model

b0001-b1111 = Reserved SBZ.

Reset value = b0000.

[7]ROTrInProgTransfer in progress. This field indicates if a transfer is currently in progress on the APB master port.

Indicates the status of the DEVICEEN input.

  • If APB-AP is connected to the Debug APB, that is, a bus connected only to debug and trace components, it must be permanently enabled by tying DEVICEEN HIGH. This ensures that trace components can still be programmed when DBGEN is LOW. In practice, it is expected that the APB-AP is almost always used in this way.

  • If APB-AP is connected to a system APB dedicated to the non-secure world, DEVICEEN must be connected to DBGEN.

  • If APB-AP is connected to a system APB dedicated to the secure world, DEVICEEN must be connected to SPIDEN.


Auto address increment and packing mode on Read or Write data access. Does not increment if the transaction completes with an error response or the transaction is aborted.

Auto address incrementing is not performed on access to banked data registers 0x10-0x1C.

The status of these bits is ignored in these cases.

b11 = Reserved

b10 = Reserved

b01 = Increment

b00 = Auto increment OFF.

Increment occurs in word steps.

Reset value = b00.

[3]--Reserved SBZ.

Size of the access to perform.

Fixed at b010 = 32 bits.

Reset value = b010.

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