Texas Instruments MSP430x4xx - Manual (Page 5)

Register Bit Conventions
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Register Bit Conventions
Each register is shown with a key indicating the accessibility of the each
individual bit, and the initial condition:
Register Bit Accessibility and Initial Condition
Key Bit Accessibility
rw Read/write
r Read only
r0 Read as 0
r1 Read as 1
w Write only
w0 Write as 0
w1 Write as 1
(w) No register bit implemented; writing a 1 results in a pulse.
The register bit is always read as 0.
h0 Cleared by hardware
h1 Set by hardware
−0,−1 Condition after PUC
−(0),−(1) Condition after POR