1336F-BRF50-AA-EN-HAS2半導體模塊，A-B使用數據
使用數據地址寄存器中包含的地址。數據傳輸繼續，直到字節計數寄存器達到0。此時(shí)，DMAC設置完成位并進(jìn)入空閑狀態(tài)除非字節中的鏈接位指示更多的表遍歷計數寄存器。
桌子行走狀態(tài)表地址和表功能代碼寄存器指向DMAC表。表5-1是一個(gè)示例。該表有兩個(gè)條目每個(gè)數據塊：數據地址和字節數。當DMAC表移動(dòng)時(shí)，它從表放入表地址寄存器，第二個(gè)長(cháng)字從將表放入字節計數寄存器。
1336F-BRF50-AA-EN-HAS2半導體模塊然后轉到數據傳輸狀態(tài)如果表遍歷導致設置鏈接位，則DMAC表數據傳輸狀態(tài)結束后再次行走。注意：DMAC表必須始終放置在32位內記憶力如果是8位或16位內存，則PCC終止在桌子行走過(guò)程中遇到。SCSI數據總線(xiàn)轉換器WD33C93連接到PCC上的單獨8位數據總線(xiàn)，并不是本地MC68030總線(xiàn)。這允許PCC收集一個(gè)通過(guò)從WD33C93，不使用處理器總線(xiàn)。當一個(gè)長(cháng)單詞是準備就緒后，芯片請求本地總線(xiàn)并傳輸。本方案減輕MC68030本地總線(xiàn)上的負載。SCSI芯片接口PCC為MC68030訪(fǎng)問(wèn)WD33C93。它使用非多路模式，這需要軟件使用WD33C93指針寄存器訪(fǎng)問(wèn)其內部寄存器。WD33C93寄存器可以間接訪(fǎng)問(wèn)通過(guò)FFFE4000美元的地址寄存器?？删幊痰未鸲〞r(shí)器PCC具有兩個(gè)16位可編程滴答定時(shí)器。計時(shí)器以編程的方式向MC68030生成周期性中斷速度周期為6.25μs至0.4秒，增量為6.25μs。這個(gè)計時(shí)器也可能被禁用。計時(shí)器中斷級別為可編程，當其中斷已確認。
using the address contained in the data address register. Data
transfers continue until the byte count register reaches 0.
At this point, the DMAC sets the done bit and enters the idle state
unless more table walking is indicated by the link bit in the byte
count register.
Table Walk State
The table address and table function code registers point to the
DMAC table. Table 5-1 is an example. The table has two entries for
each data block: the data address and the byte count.
When the DMAC table walks, it copies the first longword from the
table into the table address register, and the second longword from
the table into the byte count register. It then goes to the data transfer
state. If the table walk caused the link bit to be set, the DMAC table
walks again after the data transfer state has ended.
Note The DMAC table must always be placed within 32-bit
memory. The PCC terminates if 8-bit or 16-bit memory
is encountered during a table walk.SCSI Data Bus Converter
The WD33C93 connects to a separate 8-bit data bus on the PCC and
not to the local MC68030 bus. This allows the PCC to collect one
longword of data by transferring one byte at a time from the
WD33C93 without using the processor bus. When a longword is
ready, the chip requests the local bus and transfers it. This scheme
lightens the load on the MC68030 local bus.
SCSI Chip Interface
The PCC provides the interface for MC68030 accesses of the
WD33C93. It uses the nonmultiplexed mode which requires that
the software use the WD33C93 pointer registers to access its
internal registers. The WD33C93 registers are accessible indirectly
through the address register at $FFFE4000.
Programmable Tick Timers
The PCC features two 16-bit programmable tick timers. A timer
generates a periodic interrupt to the MC68030 at the programmed
rate. The period is 6.25 μs to 0.4 seconds in 6.25 μs increments. The
timer may also be disabled. The timer interrupt level is
programmable and it provides a status/ID vector when its
interrupt is acknowledged.
