In the first pass of the assembler, $\textsf{Machine Opcode Table}\; (\textsf{MOT})$ is used to get the opcode size of the mnemonics which is needed to increment the $\textsf{LOCCTR}$ which is needed to determine the address of the labels. The labels and their corresponding addresses go to the $\textsf{Symbol Table}$ which is thus populated during the first phase and used in the second phase whereas $\textsf{MOT}$ is not modified but just used in the two phases – in the second phase to convert menmonic to opcode.