Programming Model

Note None of the remaining registers have counterparts in the MEMC040 because they are associated with functions contained only in the MCECC pair.

Data Control Register

ADR/SIZ

 

 

1st $FFF43020/2nd $FFF43120 (16-bits)

 

 

 

 

 

 

 

 

 

 

 

BIT

31

30

 

29

28

27

26

25

24

 

 

 

 

 

 

 

 

 

 

NAME

0

0

 

DERC

ZFILL

RWCKB

0

0

0

 

 

 

 

 

 

 

 

 

 

OPER

R

R

 

R/W

R/W

R/W

R

R

R

 

 

 

 

 

 

 

 

 

 

RESET

X

X

 

1 PLS

0 PLS

0 PLS

X

X

X

 

 

 

 

 

 

 

 

 

 

RWCKB READ/WRITE CHECKBITS, when set, enables the data from the eight checkbits in this MCECC to be written and read on the local MC68060 data bus (bits 24-31 for upper MCECC, bits 8-15 for lower MCECC). This bit should be cleared for normal system operation. Note that if test software forces a single bit error to a location (line) using this function, the scrubber may correct the location before the test software gets a chance to check for the single bit error at that location. This can be avoided by disabling scrubbing and making sure that all previous scrubs have completed, before performing the test. Also note that writing bad checkbits can set the ERRLOG bit in the Error Logger Register.

The writing of checkbits causes the MCECC to perform a read-modify-write to DRAM. If the location to which check bits are being written, has a single or double bit err, data in the location may be altered by the write checkbits operation. To avoid this, it is recommended that the DERC bit also be set while the RWCKB bit is set. A suggested sequence for performing read-write checkbits is as follows:

5

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5-21

Page 311
Image 311
Motorola MVME172 manual Data Control Register