Switching Function Between Mk I Mode And Mk Ii Mode; Differences Between Mk I Mode And Mk Ii Mode - NEC MuPD754202 Datasheet

4.

SWITCHING FUNCTION BETWEEN Mk I MODE AND Mk II MODE

4.1 Differences between Mk I Mode and Mk II Mode

The µ PD754202 75XL CPU has the following two modes: Mk I and Mk II, either of which can be selected. The
mode can be switched by bit 3 of the stack bank select register (SBS).
• Mk I mode : Instructions are compatible with the 75X Series. Can be used in the 75XL CPU with a ROM
capacity of up to 16 Kbytes.
• Mk II mode: Incompatible with 75X Series. Can be used in all the 75XL CPU's including those products
whose ROM capacity is more than 16 Kbytes.
Table 4-1. Differences between Mk I Mode and Mk II Mode
Number of stack bytes
for subroutine instructions
BRA !addr1 instruction
CALLA !addr1 instruction
CALL !addr instruction
CALLF !faddr instruction
Caution The Mk II mode supports a program area exceeding 16 Kbytes for the 75X and 75XL
Series. Therefore, this mode is effective for enhancing software compatibility with
products that have a program area of more than 16 Kbytes.
The number of stack bytes (usable area) during execution of subroutine call instruc-
tions increases by 1 byte per stack compared to the Mk I mode when the Mk II mode
is selected.
However, when the CALL !addr and CALL !faddr instructions are used, the machine
cycle becomes longer by 1 machine cycle. Therefore, if more emphasis is placed on
RAM use efficiency and processing performance than on software compatibility, the
Mk I mode should be used.
12
Mk I mode
2 bytes
Not available
3 machine cycles
2 machine cycles
µ PD754202, 754202(A)
Mk II mode
3 bytes
Available
4 machine cycles
3 machine cycles