W78958B Datasheet, PDF (14/28 Pages) Winbond – 8-BIT EMULATION MICROCONTROLLER

W78958B
Standard Type, Normal Mode
If ENSTD is set to low at power-on, then the W78958B will operate as the standard type. In this type,
pins ROMS1 and ROMS0 are input pins that are used to select one of four different ROM sizes: 4, 8,
16, or 32 K bytes. When EA is set to high, an internal program code is fetched from the external 4, 8,
16, or 32 KB EPROM, depending on the state of ROMS1 and ROMS0. The interface pins needed are
DP4<7:0>, as the data bus, and AP5<7:0> and AP6<3:0>, AP6<4:0>, AP6<5:0> or AP6<6:0>, as the
address bus, again depending on the state of ROMS1 and ROMS0. When EA is set to low, the
device is compatible with W78C32 operations.
For example, when pins ROMS1 and ROMS0 are held in "L" and "H" states, respectively, the
functions of the standard type are fully compatible with those of the W78C52, except that the internal
8 KB ROM is replaced by an external EPROM. To reduce the size of the EPROM, one can use the
W78T064, a 20-pin, 300-mil 8 KB EPROM with internal address latch. If the W78T064 is used as the
EPROM, DP4<7:0> should be used as the low-byte address and data bus. And the AP7<3> (IPSEN )
enables the "internal" (lower-order 8 KB, for this example) program memory output onto the DP4
address/data bus during fetch and MOVC operations. For detailed specifications concerning the
W78T064, refer to the W78T064 product specifications.
The IPME pin indicates the access buses for the program memory. During accesses to the "internal"
program memory, it outputs "0" to indicate that the access buses are DP4, AP5, and AP6. During
accesses to the "external" program memory, it outputs "1" to indicate that the access buses are Port 0
and Port 2.
For a description of the emulation functions of the standard type, refer to the next section.
Emulation Functions (Both Types)
The W78958B supports emulation functions for the standard type (emulation of the W78C31,
W78C32, W78C51, W78C52, W78C154*, and W78C58) and the advanced type (emulation of the
W78C438, and W78C458).
When the device is operating in the normal mode, pins ESEL , CLKS1, AP7<2> ( IPME ), ROMS1 and
ROMS0 provide special functions to facilitate ICE design. When the emulation program and data
memory are combined in a single chip, ESEL is used to separate the two memory spaces. ESEL
outputs "0" to indicate that the W78958B is accessing program memory and "1" to indicate that the
W78958B is accessing data memory. CLKS1 outputs the internal S1 state cycle clock, which can be
used as a base for the necessary timing signals. When W78958B is operating as the standard type
and emulates a model that includes an internal ROM, AP7<2> ( IPME ) is used to select the "internal"
or external program memory. When the W78958B fetches the "internal" program, IPME outputs "0"
to indicate that the access buses are DP4, AP5, and AP6. When the W78958B fetches the external
program, IPME outputs "1" to indicate that the access buses are Port 0 and Port 2. Finally, in the
standard type, PSEN , Port 0, Port 2, DP4, AP5, and AP6 are used to configure the device to emulate
products with different ROM code sizes, such as the W78C51 (4 KB ROM), W78C52¡]8 KB ROM),
W78C154* (16 KB ROM), and W78C58 (32 KB ROM). Pins ROMS1 and ROMS0 are used to select
the ROM size. Concerning the functions of PSEN , Port 0, Port 2, DP4, AP5, and AP6, see tables D1
to D4.
In an ICE system, when a breakpoint condition is met or the user forces the CPU to stop running, the
W78958B's ICESET pin is forced high by the system operation. When ICESET active is sampled at
the end of the S1 state, the EMU pin is set to high to indicate that the W78958B has entered the
emulation mode. Once this occurs, the W78958B will remain in the S2 state of the instruction
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