IP82C237 datasheet(13/25 Pages) INTERSIL

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registers to operate as in normal mode (Data-Width register

not accessible) until 16-bit transfer mode is again entered.

The four mask bits may also be cleared simultaneously by

using the Clear Mask Register command (see software com-

mands section). This command has no effect on the data-

width bits.

Temporary Register - The internal Temporary register is

used to hold data during memory-to-memory transfers. Fol-

lowing the completion of the transfers, the last byte moved

can be read by the microprocessor. In the case of 16-bit

transfers, only the least signiﬁcant 8-bits of the last word

transferred are stored in this register. The Temporary regis-

ter always contains the last byte transferred in the previous

memory-to-memory operation, unless cleared by a RESET

or Master Clear.

Software Commands Affected by

16-Bit Mode

Master Clear - This software instruction has the same effect

as the hardware RESET. The Command, Status, Request,

and Temporary registers, and Internal First/Last Flip-Flop

and mode register counter are cleared and the Mask register

is set. When the Master Clear instruction occurs while in 16-

bit transfer mode, the 82C237 enters normal (8-bit) transfer

mode in the Idle cycle.

Clear Mask Register - This command clears the mask bits

of all four channels, enabling them to accept DMA requests.

This command has no effect on data-width bits in 16-bit

transfer mode.

OPERATION

IOR

IOW

Read Status Register

1000

Write Command Register

1000

Read Request Register

1001

Write Request Register

1001

Read Command Register

1010

Write Single Mask Bit (Note 1)

1010

Write All Data-Width Bits (Notes 1, 2)

1010

Read Mode Register

1011

Write Mode Register

1011

Set First/Last F/F

1100

Clear First/Last F/F

1100

Read Temporary Register

1101

Master Clear

1101

Clear Mode Reg. Counter

1110

Clear Mask Register

1110

Read All Mask/Data-Width Bits (Note 2)

1111

Write All Mask Bits

1111

NOTES:

1. The register to be written is determined by data bit 3.

2. Data-Width bits exist in 82C237, 16-bit mode only.

FIGURE 5. 16-BIT MODE SOFTWARE COMMAND CODES AND REGISTER CODES

82C237

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