The 155-0090-00 is a Tek-made custom four-decade counter IC. The die is the M059 designed by Mike Metcalf in 1974.
It contains four 4-bit BCD counters, four 4-bit latches and four BCD-to-analog converters producing a 10-level output current to interface directly with the 7000 series readout system.
- 7D01 (U1338 before SN B052815, later models use 155-0171-00)
- 7D12 (U500)
- 7B85 (U686 before SN B06000), later models use 155-0171-00/155-0185-00