Programming Model

stream". The reset serial bit stream initializes the MCECC pair by setting or resetting the bits that appear in the Defaults 1 and Defaults 2 Registers. Software can override this initial setting by writing to the Defaults Registers. It is not recommended that non-test software alter the bits in the Defaults Registers.

Programming Model

This section defines the programming model for the control and status registers (CSRs) in the MCECC pair. The base address of the CSRs is hard coded to the address $FFF43000 for the MCECC pair on the first mezzanine board and $FFF43100 for the MCECC pair on the second mezzanine board. The CSRs for the two MCECCs appear at the same address, (one on D16-D31, the other on D00-D15). Hardware automatically duplicates the values that are written to the CSRs in the upper MCECC (the one that connects to D16-D31) to the lower MCECC (the one that connects to D0-D15). Hence Software only needs to write to the control registers in the upper MCECC. This duplicating function can be disabled by software for test purposes.

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Some effort has gone into making the register map for the first eight registers, of the MCECC pair, look as close as possible to that for the eight registers contained in the MEMC040, the parity memory controller used in the MVME167 and MVME187. Where there are differences, they are noted. The remaining 18 registers contain functions unique to the MCECC pair.

The possible operations for each bit in the CSR are as follows:

RThis bit is a read only status bit.

R/W

This bit is readable and writable.

R/C

This status bit is cleared by writing a one to it.

CWriting a zero to this bit clears this bit or another bit. This bit reads zero.

SWriting a one to this bit sets this bit or another bit. This bit reads zero.

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Motorola MVME172 manual Programming Model