Branching instructions

BASSM (branch and save and set mode) and BSM (branch and set mode) are branching instructions that manipulate the PSW A-mode bit (bit 32). Programs can use BASSM when branching to modules that might have different addressing modes. Programs invoked through a BASSM instruction can use a BSM instruction to return in the caller's addressing mode. BASSM and BSM are described in more detail in Establishing linkage.

BAS (branch and save) and BASR:

Save the return address and the current addressing mode in the first operand.
Replace the PSW instruction address with the branch address.

The high-order bit of the return address indicates the addressing mode. BAS and BASR perform the same function that BAL and BALR perform in 31-bit addressing mode. In 24-bit mode, BAS and BASR put zeroes into the high-order byte of the return address register.