Intel 8237

Intel 8237 is a direct memory access (DMA) controller, a part of the MCS 85 microprocessor family.

The 8237 is a four-channel device that can be expanded to include any number of DMA channel inputs.

Each channel is capable of addressing a full 64k-byte section of memory and can transfer up to 64k bytes with a single programming.

The IBM PC AT added another 8237 in master-slave configuration, increasing the number of DMA channels from four to seven.

[2] Later IBM-compatible personal computers may have chip sets that emulate the functions of the 8237 for backward compatibility.

[5] In auto initialize mode the address and count values are restored upon reception of an end of process (EOP) signal.

[5] The terminal count (TC) signals end of transfer to ISA cards.

The transfer continues until end of process EOP (either internal or external) is activated which will trigger terminal count TC to the card.

The IBM PC AT (machine type 5170) and 100% compatibles use an 80286 CPU and a 16-bit system bus architecture.

In addition to the 8237 from the PC and XT models, a second, cascaded 8237 is added, for 16-bit DMA transfers.

The design of 8237-based DMA in PC AT compatibles was not updated with the move to the 32-bit CPUs and 32-bit system bus architectures.