UPD75P0076 datasheet(13/62 Pages) NEC

13 / 62 page

µPD75P0076

4. SWITCHING BETWEEN Mk I AND Mk II MODES

Setting a stack bank selection (SBS) register for the

µPD75P0076 enables the program memory to be switched between

the Mk I mode and the Mk II mode. This capability enables the evaluation of the

µPD750064, 750066, and 750068 using

the

µPD75P0076.

When the SBS bit 3 is set to 1: sets Mk I mode (corresponds to Mk I mode of

µPD750064, 750066, and 750068)

When the SBS bit 3 is set to 0: sets Mk II mode (corresponds to Mk II mode of

µPD750064, 750066, and 750068)

4.1 Differences between Mk I Mode and Mk II Mode

Table 4-1 lists the differences between the Mk I mode and the Mk II mode of the

µPD75P0076.

Table 4-1. Differences between Mk I Mode and Mk II Mode

Item

Mk I Mode

Mk II Mode

Program counter

PC13 to 0

Program memory (bytes)

16384

Data memory (bits)

512 x 4

Stack

Stack bank

Selectable from memory banks 0 and 1

Stack bytes

2 bytes

3 bytes

Instruction

BRA !addr1

Not provided

Provided

CALLA !addr1

Instruction

CALL !addr

3 machine cycles

4 machine cycles

execution time CALLF !faddr

2 machine cycles

3 machine cycles

Supported mask ROM versions and

Mk I mode of

µPD750064, 750066,

Mk II mode of

µPD750064, 750066,

mode

and 750068

Caution

The Mk II mode supports a program area which exceeds 16K bytes in the 75X and 75XL series. This

mode enhances the software compatibility with products which have more than 16K bytes.

When the Mk II mode is selected, the number of stack bytes used in execution of a subroutine call

instruction increases by 1 per stack for the usable area compared to the Mk I mode. Furthermore, when

a CALL !addr, or CALLF !faddr instruction is used, each instruction takes another machine cycle.

Therefore, when more importance is attached to RAM utilization or throughput than software

compatibility, use the Mk I mode.

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