Manual

Card Setup

Sealevel Systems ACB-104 Page 4

DMA Channel Selection Headers E2 & E3

Headers E2 & E3 select Direct Memory Access (DMA) mode of operation. Each channel of the Enhanced Serial

Communications Controller (ESCC) will function in half duplex or full duplex DMA modes. Full duplex means

that DMA can be used for simultaneous transmit and receive. Half-duplex DMA means that you can either transmit,

or receive with DMA, but not simultaneously. The 85230 has two signals that correspond to DMA request signals,

WAIT/REQ and DTR/REQ. E2 corresponds to the SCC signal WAIT/REQ and E3 corresponds to DTR/REQ.

WAIT/REQ and DTR/REQ can be programmed to serve as DMA request lines (DRQ) by setting the appropriate

bits in Write Register 1 and Write Register 14 in the 85230. WAIT/REQ (E2) can be programmed for Transmit or

Receive DMA transfers and DTR/REQ (E3) can be programmed for Transmit Only

. For additional information on

the programming of the 85230 please refer to the Zilog ESCC Users Manual. Please note that each DMA channel is

selected by two jumpers. Only one DMA channel may be selected for each header block.

Note: If DMA is not used, remove all of the jumpers on E2 & E2 and remove jumper at E1

0 0 1 1 2 2 3 3

Figure 4 - DMA Selection Headers E2 & E3

Note: DMA Channel 2 can only be used if the floppy disk DMA drivers are turned off. Please refer to the toolkit

disk for software examples.