Using internal nodes for liberate_ams - characterization of macro block

Hi,

I'm a new user to liberate_ams, originally doing digital IC design, using Innovus for top-level implentation of mixed-signal chips.

I'm trying to characterize a large full-custom block with digital interface and internal clock distribution. We do not have a top-level testbench for the block, so I'm going for truth-table based characterization. For a start, I want to characterize one single flip-flop which has its CLK and D inputs directly connected to inputs of the block. The output of the flip-flop is an internal node, with subsequent connectivity inside the block.

My problem now is that I can't find a way to correctly point liberate_ams to this internal node. The extracted layout node/net name is X2310/60 (netlist without parasitics, as a start).
My define_cell command looks as follows:
define_cell \
  -clock { clk } \
  -input { en  <and a few more> } \
  -output { d_out<0:1023>  <and a few more> } \
  -delay delay_template_7x6 \
  -power power_template_7x6 \
  -constraint constraint_template_3x3 \
  -internal X2310/60 \
  block_top

And the according truth-table:
table chip_en_clk_in
pins         clk    en      X2310/60
INIT         R      L       X        
en_RISE      R      1       C        
en_FALL      R      0       C        
endtable

When I run char_ams (with the -user_arcs_only option) I get the following output:

...
(AMS-info) - Start Macro Characterization ...
(AMS-warning) - no wire exists for bus' pin: X2310/60
(AMS-warning) - no wire exists for bus' pin: X2310/60
             Skipping table chip_en_clk_in
(AMS-error) - at least 1 transition for 1 wire must be specified - please check table: constraint.tbl
             If this is a power table, set 'mx_power_leakage_table_vector_ratio' to 20 or more - max 100
             If using define_deck command, make sure the -dut_inst instance name exists and is correct
...

I also tried specifying pin names of hierarchical instances to no avail - so I couldn't find a way to put that constraint on this internal node.

I'd be glad if somebody could tell me how to setup such internal nodes correctly - or whether this is the correct way of setting this up at all... sorry for that potentially silly question...

Andreas