Z16M1720ASG1868 Zilog, Z16M1720ASG1868 Datasheet - Page 68

• Manufacturer Part Number: Z16M1720ASG1868
• Description: IC PCMCIA INTERFACE 100-VQFP
• Manufacturer: Zilog

Specifications of Z16M1720ASG1868

• Applications: *
• Interface: *
• Voltage - Supply: *
• Package / Case: 100-LQFP
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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port’s Ready line goes inactive before this occurs, the DMA pauses until
the Ready line comes active again. This is also called Block mode.
In all modes, the operation on the byte is completed in an orderly fashion
when a byte of data is read into the DMA, regardless of the state of other
signals (including a port’s Ready line). Figure 20 illustrates the sequence of
events that occur in a sequential transfer/search of one byte, whatever of the
mode of operation. First, the source port address is incremented or decre-
mented, if it was programmed to be a variable-address port. Then, the byte
is read from that port to the DMA. Next, the destination port address is
incremented or decremented, if it was programmed to be a variable. The
byte is then written to the destination port. If a search capability is included,
the byte is compared to the match byte. When no byte match occurs, the
DMA increments the byte counter and continues. When a byte is found, a
status bit is set and the DMA either continues by incrementing the byte
counter, stops (releases the bus), or interrupts the CPU, depending on its
initial programming. The next three figures illustrate how the three modes
function before, during, and after the single-byte operation, which is shown
in Figure 20.
Operation in the Byte mode (Figure 21) begins with an enabling command
from the CPU and a test of the I/O device’s Ready line. When the Ready
line is active, the DMA requests the system bus (address, data, and control
buses) through the Bus Request line, and the CPU acknowledges and
releases control to the DMA. The transfer of and/or search of one byte takes
place as in Figure 20. Then, a test is made for end-of-block by checking to
see if the byte counter has reached the programmed block length. If the end
is not reached, the DMA releases the bus back to the CPU. If the end is
reached, a status bit is set and some terminating action occurs, according to
the initial programming. Releasing the bus between each byte allows the
CPU to execute at least one machine cycle before releasing the bus again to
the DMA for the next byte transfer. This means that while the DMA
operates more slowly than it could in other modes, CPU activities like
interrupt acknowledgement, polling, and memory refresh can be inter-
leaved with DMA transfers in the Byte mode.
Direct Memory Access