AMD Am188TMER, Am186TMER user manual Slave Mode Operation, Slave Mode Interrupt Nesting

8.4SLAVE MODE OPERATION

When Slave mode is used, the microcontroller’s internal interrupt controller is used as a slave controller to an external master interrupt controller. The internal interrupts are monitored by the internal interrupt controller, while the external controller functions as the system master interrupt controller.

On reset, the microcontroller is in Master mode. To activate Slave mode operation, bit 14 of the Relocation Register must be set (see Figure 4-2 on page 4-4).

Because of pin limitations caused by the need to interface to an external 82C59A master, the internal interrupt controller does not accept external inputs. However, there are enough interrupt controller inputs (internally) to dedicate one to each timer. In Slave mode, each timer interrupt source has its own mask bit, IS bit, and control word.

The INT4, watchdog timer, and serial port interrupts are not available in Slave mode. In Slave mode, each peripheral must be assigned a unique priority to ensure proper interrupt controller operation. The programmer must assign correct priorities and initialize interrupt control registers before enabling interrupts.

8.4.1Slave Mode Interrupt Nesting

Slave mode operation allows nesting of interrupt requests. When an interrupt is acknowledged, the priority logic masks off all priority levels except those with equal or higher priority.

8.4.2Slave Mode Interrupt Controller Registers

The Interrupt Controller Registers for Slave mode are shown in Table 8-5.All registers can be read and written, unless specified otherwise.

Table 8-5	Interrupt Controller Registers in Slave Mode
		Register
	Offset	Mnemonic	Register Name	Affected Pins	Comments
	3Ah	T2INTCON	Timer 2 Interrupt Control		Interrupt Type XXXXX101
	38h	T1INTCON	Timer 1 Interrupt Control	TMRIN1	Interrupt Type XXXXX100
				TMROUT1
	36h	DMA1CON	DMA 1 Interrupt Control		Interrupt Type XXXXX011
	34h	DMA0CON	DMA 0 Interrupt Control		Interrupt Type XXXXX010
	32h	T0INTCON	Timer 0 Interrupt Control	TMRIN0	Interrupt Type XXXXX000
				TMROUT0
	30h	INTSTS	Interrupt Status
	2Eh	REQST	Interrupt Request		Read Only
	2Ch	INSERV	In-Service		Read Only
	2Ah	PRIMSK	Priority Mask
	28h	IMASK	Interrupt Mask
	22h	EOI	Specific EOI		Write Only
	20h	INTVEC	Interrupt Vector

Interrupt Control Unit 8-29