256 Kbit OTP ROM, 150 ns, PDIP28
The Texas Instruments TMS27PC256-15NE is a 256 Kbit (32K x 8) one-time programmable (OTP) ROM with a 150 ns access time, housed in a 28-pin PDIP package. This is a factory-programmed memory — the OTP array is written during manufacturing and cannot be erased or rewritten in the field. The 150 ns access time sets the read-cycle ceiling for the bus it connects to — a microcontroller or ASIC with a memory controller that expects sub-100 ns access may need wait states inserted to meet the timing. For legacy 8- or 16-bit systems that were designed around 150 ns EPROMs, this is a direct drop-in.
Active production, RoHS non-compliant
Note that this part is RoHS non-compliant (leaded solder terminations). For BOMs that require RoHS compliance, a lead-free alternative would need a board-spin or a different package variant — this is a legacy part intended for existing designs that tolerate tin-lead solder.
What it swaps into on site
The PDIP28 package is socket-friendly — it can be swapped in the field with a standard IC puller and a DIP socket, no hot-air station needed. Pin 1 orientation is marked by a notch and a dot on the package body; the socket orientation is unambiguous as long as the notch aligns with the socket's key. Because it is OTP, there is no UV-erase window — the package is solid epoxy, which makes it more mechanically robust than a ceramic-window EPROM for field handling. No special ESD precautions beyond the usual bench mat are required, though the part is CMOS and sensitive to latch-up if input voltages exceed the supply rails.