Am186™CC/CH/CU Microcontrollers User’s Manual
5-1
CHAPTER
5
CHIP SELECTS
5.1
OVERVIEW
Signals that allow the CPU to select specific memory or peripheral devices are called
chip
selects.
The microcontroller provides six chip select outputs for use with memory devices (UCS,
LCS, and MCS3–MCS0) and eight chip selects for use with peripherals (PCS7–PCS0) in
either memory or I/O space. The six memory chip selects can be used to address three
memory ranges. Each peripheral chip select addresses a 256-byte block offset from a
programmable base address in memory or I/O.
The microcontroller can sense a ready signal for each of the memory or peripheral chip
select lines. The R2 bit in each of the memory chip select control registers determines
whether the external ready signal is required or ignored.
In addition, the R1–R0 bits in each of the memory chip select control registers control the
number of wait states inserted in the bus cycle. Although most memory and peripheral
devices can be accessed with three or fewer wait states, some slower devices cannot. This
feature allows devices to use externally generated wait states to slow down the bus.
Address and data bus size options and enabling or disabling the address bus during the
address phase of a bus cycle are configured on a chip select basis. UCS and LCS can also
be configured for DRAM support.
The chip select lines are active for all memory and I/O cycles in their programmed areas,
whether they are generated by the CPU or by the integrated DMA unit.
The UCS and LCS chip selects assert relative to the timing of the nonmultiplexed address
(A) bus; the MCS and PCS chip selects assert relative to the multiplexed address and data
(AD) bus. The timing for chip selects is shown in the data sheets for each of the Am186CC/
CH/CU microcontrollers.
The CAS0 and CAS1 signals can be used to perform byte writes in a manner similar to
WLB and WHB, respectively. That is, CAS0 corresponds to the low byte (WLB) and CAS1
corresponds to the high byte (WHB).
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...