The W78958B is packaged in a 100-pin PQFP and is available in two different types, standard and advanced. The standard type supports the functions of the W78C31, W78C32, W78C51, W78C52, W78C154*, and W78C58. The advanced type supports the functions of the W78C438 and W78C458. Both types can be operated in two modes, normal and emulation. In normal mode, the W78958B runs freely, like the W78C51 family of products. In emulation mode, which is entered by driving the ICESET pin high asynchronously, the W78958B stays in the S2 state of the next instruction. In this mode, the W78958B allows direct access (read/write) to the special function registers (SFRs), the program counter (PC), and the internal RAM. Also, it allows ICE makers to access the external program and data memory easily, thereby eliminating the need for glue logic. Moreover, it provides several signals to facilitate ICE design, including IPME (Internal Program Memory Enable), for switching between "internal" and external ROM, ESEL (Emulation address space Select), for combining the emulation program and data memory in a 128 KB SRAM, and CLKS1 (internal S1 state clock timing signal), for creating the emulation control signals. Once the ICESET pin goes low, the W78958B will release its internal clock and return to its normal operating mode. For detailed specifications concerning the W78C31, W78C32, W78C51, W78C52, W78C154*, W78C58, W78C438, and W78C458, refer to the Functional Description below or to the Winbond product specifications.