Emulator Support
Am186™CC/CH/CU Microcontrollers User’s Manual
4-3
186 processors also use BHE with A0 to denote refresh cycles to 16-bit DRAM (both
inactive). The Am186CC/CH/CU microcontrollers do not support 8-bit wide DRAM designs,
so using this mechanism to determine refresh cycles is reliable under all allowed DRAM
designs.
4.3.2.4
ALE
In multiplexed bus mode, ALE indicates that a valid address is on the AD bus. Some
emulators may require this signal. In most instances, an active chip select signal can also
be used to indicate a valid address.
4.3.2.5
ARDY and SRDY
If the target requires ready signals to operate, ARDY and SRDY cannot be used as PIOs.
Some emulators give the user control over the external ready target requirement. For
instance, ready may be required by the emulator to match overlay memory speeds to faster
target wait-state setups.
4.3.2.6
BHE
See “{ADEN}/BHE” on page 4-2.
4.3.2.7
BSIZE8
The absence of BHE for 8-bit memory regions when an emulator design uses 16-bit overlay
memory for a memory region defined as 8 bits wide poses problems for an emulator. The
emulator must know when memory accesses are targeted at 8-bit regions to correctly steer
the data between the low half of the data bus and the high half of the data bus. Although it
is possible to snoop all events that determine the memory width (chip select pulldowns
during reset, and UMCS, LMCS and MPCS register accesses), these methods can be
unreliable. The Am186CC/CH/CU microcontrollers’ BSIZE8 pin unambiguously signals the
intended size of the memory region during external bus cycles.
4.3.2.8
[CAS1–CAS0] and [RAS1–RAS0]
The on-chip DRAM controller can be configured to work with DRAM in the lower (LCS) or
upper (UCS) memory regions. The emulator needs to reconstruct the address used during
an access. The CAS signal can come too late for fast address generation. However, the
complete address appears on the A19–A0 bus during the RAS cycle. Additionally, because
the full address bus is nonmultiplexed, it is a simple task to identify an access to the DRAM
region.
CAS-before-RAS cycles could also be used to determine if an access is a refresh, but the
late arrival of the RAS signal makes this problematic.
The DRAM can only be accessed in 16-bit mode. This eliminates the problem of determining
object size due to dynamic bus sizing.
4.3.2.9
CLKOUT
The internal processor clock can be sent out on the CLKOUT pin. Emulators generally
require this.
4.3.2.10
LCS
The system uses LCS as a RAM chip select. Emulators use this to determine when RAM
accesses occur, and can intercept it for overlay memory purposes.
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...