Memory Types and Properties

Area Description Accessed as Bit Accessed as Byte Accessed as Word Accessed as Dword Can be Retentive Can be Forced

I Discrete inputs and image register read/write read/write read/write read/write no yes
Q Discrete outputs and image register read/write read/write read/write read/write no yes
M Internal memory bits read/write read/write read/write read/write yes yes
SM Special memory bits (SM0 - SM29 are read-only) read/write read/write read/write read/write no no
V Variable memory read/write read/write read/write read/write yes yes
T Timer currents and Timer bits T-bit
read/write
no T-current
read/write
no T-current - yes T-bit - no no
C Counter currents and Counter bits C-bit
read/write
no C-current
read/write
no C-current - yes C-bit - no no
HC High-speed counter currents no no no read only no no
AI Analog inputs no no read only no no yes
AQ Analog outputs no no write only no no yes
AC Accumulator registers no read/write read/write read/write no no
L Local variable memory read/write read/write read/write read/write no no
S SCR read/write read/write read/write read/write no no