Atmel SpaceWire Router SpW-10X - Manual (Page 68)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
68
Mask
Length
4 bytes for the mask to modify a 32-bit register.
Header
CRC
The header CRC used to detect errors in the header part of the command
packet.
1
Data and
Mask
The data and mask values to write to the SpaceWire router. The data is
written dependent on the mask as shown in Figure 7-8.
8
Data and
Mask CRC
The data and mask CRC used to detect errors in the data part of the
command packet.
1
A Read-Modify-Write command modifies the bits of a SpaceWire router register dependent on the
contents of the register (Register Data), the command data (Command Data) and the command mask
value (Mask) as follows:
Register Value = (Mask AND Command Data) OR (NOT Mask AND Register Data)
An example is shown below, the highlighted bits are set or reset by the command.
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
31 23
0 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0
15 0 7
Command Data
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
31 23
1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
15 0 7
Command Mask
1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
31 23
1 0 1 0 0 1 0 0 0 0 0 0 1 0 1 0
15 0 7
Register Data
Returned to source
1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
31 23
0 1 1 0 0 0 1 1 0 0 0 0 1 0 1 0
15 0 7
Data Written to Register
(Mask AND Command Data) OR (NOT Mask and Register Data)
Figure 7-8 Read-Modify-Write example operation