4.1.1Peripheral Control Block Relocation Register (RELREG, Offset FEh)

The peripheral control block is mapped into either memory or I/O space by programming the Peripheral Control Block Relocation (RELREG) Register (see Figure 4-2). This register is a 16-bit register at offset FEh from the control block base address. The RELREG Register provides the upper 12 bits of the base address of the control block. The control block is effectively an internal chip select range.

Other chip selects can overlap the control block only if they are programmed to zero wait states and ignore external ready. If the control register block is mapped into I/O space, the upper four bits of the base address must be programmed as 0000b (because I/O addresses are only 16 bits wide).

In addition to providing relocation information for the control block, the RELREG Register contains a bit that places the interrupt controller into either Slave mode or Master mode.

At reset, the RELREG Register is set to 20FFh, which maps the control block to start at FF00h in I/O space. An offset map of the 256-byte peripheral control register block is shown in Figure 4-1.

Figure 4-2 Peripheral Control Block Relocation Register (RELREG, offset FEh)

15

7

0

R19–R8

S/M M/IO

Res Res

The value of the RELREG Register is 20FFh at reset.

Bit 15: Reserved

Bit 14: Slave/Master (S/M)—Configures the interrupt controller for Slave mode when set to 1 and for Master mode when set to 0.

Bit 13: Reserved

Bit 12: Memory/IO Space (M/IO)—When set to 1, the peripheral control block (PCB) is located in memory space. When set to 0, the PCB is located in I/O space.

Bits 11–0: Relocation Address Bits (R19–R8) —R19–R8 define the upper address bits of the PCB base address. The lower eight bits (R7–R0) default to 00h. R19–R16 are ignored when the PCB is mapped to I/O space.

4-4

Peripheral Control Block

Page 62
Image 62
AMD Am186TMER, Am188TMER user manual Bit 15 Reserved, Bit 13 Reserved