Configuration Basics
2-4
Am186™CC/CH/CU Microcontrollers User’s Manual
2.2.3
Peripheral Registers
While the 186-legacy registers can be accessed directly through the 186 instructions, the
peripheral registers must be accessed by using instruction operands that access memory
or I/O space.
The address of each 16-bit read/write peripheral register is in the internal 1-Kbyte peripheral
control block (PCB). Registers physically reside in the peripheral devices they control, but
they are addressed through the PCB. This block resides either in memory or I/O space, at
the location pointed to by the Peripheral Control Block Relocation (RELOC) register (see
Table 2-2). Because the base address of the block can change, the address of each register
is specified as an offset from the location pointed to by the RELOC register, rather than as
an absolute address. To determine the absolute address of the register in memory or I/O
space, add the offset to the base address. For a discussion of memory versus I/O space,
see “Memory Organization and Address Generation” on page 2-5.
Note: Accesses to the PCB should be performed by direct processor actions. The use of
DMA to write or read from the PCB results in unpredictable behavior, except where explicit
exception is made to support a peripheral function, such as the High-Speed UART transmit
and receive data registers.
The PCB base address can be set to any even 1-Kbyte boundary in memory or I/O space
(i.e., the lower 10 bits of the base address must be 0). RELOC resides in the last register
address of the PCB, at offset 03FEh. On an external or watchdog timer reset, the RELOC
register value is set to 20FCh, which maps the PCB to start at FC00h in I/O space. This
places the RELOC register at FFFEh. Appendix A, “Register Summary,” provides a
summary of PCB registers in offset order, including default address locations. For a
complete description of the RELOC register, see the
Am186™CC/CH/CU Microcontrollers
Register Set Manual, order #21916.
A legacy feature on the Am186CC/CH/CU microcontrollers allows logical word writes to
the PCB registers to be performed as byte writes on the external bus. These writes transfer
16 bits of data to the PCB register even if an 8-bit register is named in the instruction. For
example, “out dx, al” writes the value of AX to the port address in DX. Reads to the PCB
registers should always be done as word reads. This feature eliminates the need for an
additional bus cycle when the same code is executed on an 8-bit Am188 device or when
the PCB overlaps an 8-bit address space. Unaligned reads and writes to the PCB result in
unpredictable behavior on the Am186CC/CH/CU microcontrollers.
Internal logic recognizes control block addresses and responds to bus cycles. During bus
cycles to internal registers, the bus controller signals the operation externally (i.e., the RD,
WR, status, address, and data lines are driven as in a normal bus cycle), but the data bus,
SRDY, and ARDY are ignored.
Table 2-3 lists the peripheral registers by functional groupings, along with the address offset
where the group begins. For detailed information about the peripheral registers, refer to the
Am186™CC/CH/CU Microcontrollers Register Set Manual, order #21916.
Table 2-2
Configuration Register Summary
Offset
Register
Mnemonic
Register Name
Description
3FEh
RELOC
Peripheral Control Block Relocation
Allows software to relocate the peripheral
control block to start at any even 1024-byte
location in either memory or I/O space.
Содержание Am186 CC
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Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
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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...