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7.1 Overview
The H8/3048 Series has an on-chip refresh controller that enables direct connection of 16-bit-wide
DRAM or pseudo-static RAM (PSRAM).
DRAM or pseudo-static RAM can be directly connected to area 3 of the external address space.
A maximum 128 kbytes can be connected in modes 1, 2 and 5 (1-Mbyte modes). A maximum
2 Mbytes can be connected in modes 3, 4, and 6 (16-Mbyte modes).
Systems that do not need to refresh DRAM or pseudo-static RAM can use the refresh controller as
an 8-bit interval timer.
When the refresh controller is not used, it can be independently halted to conserve power. For
details see section 20.6, Module Standby Function.
7.1.1 Features
The refresh controller can be used for one of three functions: DRAM refresh control, pseudo-static
RAM refresh control, or 8-bit interval timing. Features of the refresh controller are listed below.
Features as a DRAM Refresh Controller
•
Enables direct connection of 16-bit-wide DRAM
•
Selection of 2CAS or 2WE mode
•
Selection of 8-bit or 9-bit column address multiplexing for DRAM address input
Examples:
— 1-Mbit DRAM: 8-bit row address × 8-bit column address
— 4-Mbit DRAM: 9-bit row address × 9-bit column address
— 4-Mbit DRAM: 10-bit row address × 8-bit column address
CAS-before-RAS refresh control
•
•
Software-selectable refresh interval
•
Software-selectable self-refresh mode
•
Wait states can be inserted
Features as a Pseudo-Static RAM Refresh Controller
RFSH signal output for refresh control
•
•
Software-selectable refresh interval
•
Software-selectable self-refresh mode
•
Wait states can be inserted
Section 7 Refresh Controller
147
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