CD1284 Datasheet, PDF (33/176 Pages) Intel Corporation – IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports

IEEE 1284-Compatible Parallel Interface Controller — CD1284
5.2
5.2.1
As described above, Channel 0 is a separate entity comprised of its own FIFO and DMA data
interface, as well as a high-speed state machine that handles all of the modes defined in the IEEE
STD 1284 specification. Channel 0 performs the slave, or peripheral, function of the IEEE STD
1284 interface and can be programmed to accept negotiations into any or all of the defined modes.
The MPU aids the parallel port by providing the local access (through the CAR) and provides
interrupt support (generation and response). However, this is the only action where the MPU is
involved in parallel port service-request activities.
CPU Interface
The CPU interface comprises an 8-bit bidirectional data bus, a 7-bit address bus, a 16-bit DMA
port and control inputs to identify the type of I/O cycle occurring. Although the strobe names and
basic timing match that of the Motorola^ 68000 family, the CD1284 fits easily into any CPU
environment.
In most cases, when the CPU reads or writes an internal CD1284 location, it actually accesses a
location in a RAM array to serve as a bank of registers. Some locations however, are mapped to
actual hardware resources for example, when a hard output signal is required (such as a service-
request output in the SVRR) or when it is necessary to read the actual state of an input (such as a
modem input).
The CD1284 is a synchronous device. All internal operations occur on edges and levels (phases) of
the internal clock. The internal clock is generated by dividing the external (system) clock by two.
When the CPU performs an I/O cycle with the CD1284, it strobes; address, and data are sampled
on the rising edges of the internal clock. As illustrated in Chapter 8.0, the external control signals
must meet setup times with respect to system clock edges. Once a cycle starts, the sequence of
events is locked to the clock of the CD1284. With events (address setup, write data setup, and read
data available) occurring at predictable times.
It is not necessary to design a synchronous interface to the CD1284. In an asynchronous design, the
DTACK* (Data Transfer Acknowledge) signal indicates that the CD1284 has completed the
requested data transfer for all I/O cycles except DMA. DTACK* can be an input to wait-state
generation logic that pauses the CPU until the operation is complete. If the CS* and DS* strobes
(Chip Select and Data Strobe) do not meet the minimum setup time with respect to the system
clock edge, the CD1284 does not detect the I/O request, and the cycle delays for two full-system
clock cycles, meeting the setup time. The I/O cycle commences and follows the predictable timing
with DTACK* signaling the end.
Read Cycles
Read cycles are initiated when both the CS* and DS* inputs are activated and the R/W* (read/
write) input is high. All strobes and address inputs must meet the setup times as specified in
Chapter 8.0. Both the CS* and DS* signals must be valid for a cycle to start. Cycle times are
measured from whichever of the two signals goes active last. The CD1284 signals the completion
of the read cycle (placing the data from the addressed register on the data bus pins) by activating
DTACK*. The read cycle terminates when the CPU removes CS* and DS*.
Datasheet
33