The maximum number of SDCCH/8s you can define in an ericsson cell is 32.
However, there is also a limitation on the maximum number of SDCCHs you can define per TRX, defined by the BSC parameter MAXNOSDCCHTRX which has a range of 1-4.
The multiplexing/concentration method you use on the abis also puts a limitation on the number of SDCCHs you can define per TRX. For TRX signalling going through unconcentrated abis timeslots with throughputs 64, 32 or 16kbps, the maximum number of SDCCHs per TRX are respectively 4,2 and 1. For concentration factors of 4,3 or 2 (on a 64kbps abis), the maximum number of SDCCH per TRX are respectively 2,3 and 4.
Let me know if you need any further explanation.