Am186™CC/CH/CU Microcontrollers User’s Manual
6-1
CHAPTER
6
DRAM CONTROLLER
6.1
OVERVIEW
Dynamic Random Access Memory (DRAM) offers memory at moderate speed and low
cost. DRAM memory cells consist of one transistor and one capacitor. DRAM also uses a
multiplexed address bus in a row/column format, which results in a lower pin count and
smaller device package.
DRAM is volatile; that is, if the capacitors for the memory cells are not periodically recharged,
the contents of memory is lost. The process of periodically recharging the capacitors is
called refresh.
The DRAM controller’s purpose is to use the processor’s address, status, and control lines
to generate the multiplexed address strobes. The Row Address Strobe (RAS) and Column
Address Strobe (CAS) signals latch the row and column addresses inside the DRAM.
To support DRAM, the Am186CC/CH/CU microcontrollers each have a fully integrated
DRAM controller that provides a glueless interface to 40-ns, 50-ns, 60-ns, and 70-ns
Extended Data Out (EDO) DRAM (EDO DRAM is sometimes called Hyper-Page Mode
DRAM). Up to two banks of 4-Mbit (256 Kbit x 16 bit) DRAM can be accessed. Page Mode,
Fast Page Mode (FPM), Asymmetrical, and 8-bit wide DRAM are not supported.
The Am186CC/CH/CU microcontrollers support the most common DRAM refresh option,
CAS-Before-RAS. All refresh cycles contain three wait states to support the DRAMs at
various frequencies. The DRAM controller never performs a burst access. All accesses are
single accesses to DRAM. If the PCS chip selects are decoded to be in the DRAM address
range, PCS accesses take precedence over the DRAM.
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...