Tandy 1000 SL Technical Reference Manual page 112

8 2 3 7 ~
(a237~, a237~-4,8237~-5)
U
HIGH PERFORMANCE
PROGRAMMABLE DMA CONTROLLER
Enabie/Dlsable Control of Individual
DMA Requests Channels
Four independent DMA Channels
Transfers
Independent Autoinitialization of Ail
Channels
w
Software DMA Requests
Memory-to-Memory Transfers
w
Independent Polarity Control for DREQ
Memorv Block initialization
8
Directly Expandable to Any Number of
End of Proce8.s input for Termlnating
and DACK Signals
8
Available
in
EXPRESS
8
Available
In
IO-Lead Cerdlp and Plastic
Address Increment or Decrement
High Performance: Transfers up to
1.6M Bytes/&cond with MHz 823715-5
-
Standard Temperature Range
Packages
(See P*ging Spec. Order r231369)
The 8237A Multimode Direct Memory Access (DMA) Controller is a peripheral interface circuit for microproc-
essor systems. It is designed to improve system performance by allowing external devices to directly transfer
information from the system memory. Memory-to-memory transfer capability is also provided. The 8237A
offers a wide variety of programmable control features to enhance data throughput and system optimization
and to allow dynamic reconfiguration under program control.
The 8237A is designed to be used in conjunction with an external 8-bit address latch. It contains four indepen-
dent channels and may be expanded to any number of channels by cascading additional controller chips. The
three basic transfer modes allow programmability of the
types of DMA service by the user. Each channel can
be individually programmed to Autoinitialize to its original condition following an End of Process
(m).
Each
channel has a full
64K
address and word count capability.
The 8273A-4 and 8237A-5 are 4 MHz and 5 MHz versions of the standard 3 MHz 8237A respectively.
231466-1
Figure 1. Block Diagram
231406-2
Figure 2. Pin
Cont lguration
2-234