Yamaha PM1D Supplementary Manual page 6

PM1D System Software V1.6 Supplementary Manual
However for ST IN channels, the combinations that could be assigned to the panel were limited to the following four
possibilities.
This limitation has been removed in V1.6. For example, any two ST IN channels of consecutive number such as ST IN
channels 1/2 and 5/6, or 1/2 and 7/8, can be combined freely. Also, if necessary, you may assign combinations of the same
ST IN channel to upper and lower ST IN blocks; e.g., ST IN channels 1/2 and 1/2, or ST IN channels 5/6 and 5/6.
6
The four combinations that were possible in V1.5
ST IN ST IN
block 2 block 2
3 4 1 2
1 2 3 4
ST IN ST IN
block 1 block 1
ST IN ST IN
block 2 block 2
7 8 5 6
5 6 7 8
ST IN ST IN
block 1 block 1