I am now using the S12ZVC12F0VKH. I tried to route the TXCAN0/RXCAN0 to pin PS3/2 while at the same time route TXD0/RXD0 to pin PS1/0. I set the MODRR0_M0C0RR = 0b110 and MODRR0_SCI0RR = 1. When I test on the S12ZVC-DEVKIT, the MSCAN works well while SCI0 does not work. According to the figure 2-2 on S12ZVC_RM.pdf, I wonder if the PS1/2 are routed to CPTXD0/CPRXD0 and can not be routed to SCI0 in the way I set the registers.