UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 16

• Manufacturer Part Number: UPD75238GJ
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC [NEC]

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2. ARCHITECTURE AND MEMORY MAP OF THE PD75238
(a) Data memory bank configuration
(b) General register bank configuration
(c) Memory-mapped I/O
2.1 DATA MEMORY BANK CONFIGURATION AND ADDRESSING MODES
at addresses 000H to 19FH and 200H to 3FFH, a display data memory (96 words
to 1FFH, 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 PD75238 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 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 PD75238 has three architectural features:
Each of these features is explained below.
As shown in Fig. 2-1, the data memory space of the PD75238 contains a static RAM (928 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
MBE = 0 mode
MBE = 1 mode
• Interrupt processing
• Processing that repeats internal hardware and static RAM operations
• Subroutine processing
• Usual program processing
Applicable program processing
4 bits) at addresses 1A0H
PD75238
4 bits)