UPD75518 NEC, UPD75518 Datasheet - Page 15

• Manufacturer Part Number: UPD75518
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

2. ARCHITECTURE AND MEMORY MAP OF THE PD75518(A)
(a) Data memory bank configuration
(b) General register bank configuration
(c) Memory-mapped I/O
2.1 DATA MEMORY BANK CONFIGURATION AND ADDRESSING MODES
bits) at addresses 000H to 3FFH and peripheral hardware (such as I/O ports and timers) at addresses F80H to
FFFH. To address a 12-bit address in this data memory space, the PD75518(A) uses such a memory bank
configuration that the low-order eight bits are specified with an instruction directly or indirectly, and the high-
order four bits are used to specify a memory bank (MB).
are contained, allowing the addressing indicated in Fig. 2-1 and 2-2 and Table 2-1. (The MBS is a register used
to select a memory bank, and can be set to 0, 1, 2, 3, or 15. The MBE is a flag used to determine whether a
memory bank selected using the MBS register is to be enabled. The MBE is automatically saved or restored
at the time of interrupt processing or subroutine processing, so that it can be freely set in interrupt processing
and subroutine processing.)
bank specified by the MBS is operated. However, the MBE = 0 mode or the MBE = 1 mode can be selected
for each step of program processing for more efficient programming.
The PD75518(A) has three architectural features:
Each of these features is explained below.
As shown in Fig. 2-1, the data memory space of the PD75518(A) contains a static RAM (1024 words
To specify a memory bank (MB), a memory bank enable flag (MBE) and memory bank select register (MBS)
In addressing data memory space, the MBE is usually set to 1 (MBE = 1), and the static RAM in the memory
The MBE and MBS are set as indicated below.
Example
MBE = 0 mode
MBE = 1 mode
SET1 MBE
CLR1 MBE
SEL MB0
SEL MB1
SEL MB15
• Interrupt processing
• Processing that repeats internal hardware and static RAM operations
• Subroutine processing
• Usual program processing
; MBE
; MBE
; MBS
; MBS
; MBS
1
0
0
1
15
Applicable program processing
PD75518(A)
15
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