Intel 80C186EA DMA Control Unit, Chip-Select Unit, Refresh Control Unit, Power Management

PCB	Function
Offset
20H	Interrupt Vector
22H	Specific EOI
24H	Reserved
26H	Reserved
28H	Interrupt Mask
2AH	Priority Mask
2C	In-Service
2E	Interrupt Request
30	Interrupt Status
32	TMR0 Interrupt Control
34	DMA0 Interrupt Control
36	DMA1 Interrupt Control
38	TMR1 Interrupt Control
3A	TMR2 Interrupt Control
3C	Reserved
3E	Reserved

Figure 4. 80C186EA Slave Mode Peripheral

Control Block Registers

DMA Control Unit

The 80C186EA DMA Contol Unit provides two inde- pendent high-speed DMA channels. Data transfers can occur between memory and I/O space in any combination: memory to memory, memory to I/O, I/O to I/O or I/O to memory. Data can be trans- ferred either in bytes or words. Transfers may pro- ceed to or from either even or odd addresses, but even-aligned word transfers proceed at a faster rate. Each data transfer consumes two bus cycles (a mini- mum of eight clocks), one cycle to fetch data and the other to store data. The chip-select/ready logic may be programmed to point to the memory or I/O space subject to DMA transfers in order to provide hardware chip select lines. DMA cycles run at higher priority than general processor execution cycles.

80C186EA/80C188EA, 80L186EA/80L188EA

Chip-Select Unit

The 80C186EA Chip-Select Unit integrates logic which provides up to 13 programmable chip-selects to access both memories and peripherals. In addi- tion, each chip-select can be programmed to auto- matically terminate a bus cycle independent of the condition of the SRDY and ARDY input pins. The chip-select lines are available for all memory and I/O bus cycles, whether they are generated by the CPU, the DMA unit, or the Refresh Control Unit.

Refresh Control Unit

The Refresh Control Unit (RCU) automatically gen- erates a periodic memory read bus cycle to keep dynamic or pseudo-static memory refreshed. A 9-bit counter controls the number of clocks between re- fresh requests.

A 9-bit address generator is maintained by the RCU with the address presented on the A9:1 address lines during the refresh bus cycle. Address bits A19:13 are programmable to allow the refresh ad- dress block to be located on any 8 Kbyte boundary.

Power Management

The 80C186EA has three operational modes to con- trol the power consumption of the device. They are Power Save Mode, Idle Mode, and Powerdown Mode.

Power Save Mode divides the processor clock by a programmable value to take advantage of the fact that current is linearly proportional to frequency. An unmasked interrupt, NMI, or reset will cause the 80C186EA to exit Power Save Mode.

Idle Mode freezes the clocks of the Execution Unit and the Bus Interface Unit at a logic zero state while all peripherals operate normally.

Powerdown Mode freezes all internal clocks at a logic zero level and disables the crystal oscillator. All internal registers hold their values provided VCC is maintained. Current consumption is reduced to tran- sistor leakage only.

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