NEC PD78055 Benutzerhandbuch

The memory to be manipulated in the fixed space is directly addressed with 8-bit data in an instruction word.

The fixed space to which this address is applied is a 256-byte space of addresses FE20H through FF1FH.  An

internal high-speed RAM and a special-function register (SFR) are mapped at FE20H to FEFFH and FF00H to

FF1FH, respectively.

The SFR area (FF00H through FF1FH) to which short direct addressing is applied is a part of the entire SFR

area.  To this area, ports frequently accessed by the program, and the compare registers and capture registers

of timer/event counters are mapped.  These SFRs can be manipulated with a short byte length and a few clocks.

When 8-bit immediate data is at 20H to FFH, bit 8 of an effective address is set to 0.  When it is at 00H to 1FH,

bit 8 is set to 1.  Refer to [Illustration] on next page.

Identifier

Description

saddr

Label of FE20H to FF1FH immediate data

saddrp

Label of FE20H to FF1FH immediate data (even address only)

15

0

Short Direct Memory

Effective Address

1

1

1

1

1

1

1

8 7

0

7

OP code

saddr-offset

α

MOV 0FE30H, #50H;  when setting saddr to FE30H and immediate data to 50H

Operation code

0 0 0 1 0 0 0 1

OP code

0 0 1 1 0 0 0 0

30H (saddr-offset)

0 1 0 1 0 0 0 0

50H (immediate data)

When 8-bit immediate data is 20H to FFH, 

α 

= 0

When 8-bit immediate data is 00H to 1FH, 

α 

= 1