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SA-1100 Developer’s Manual 10-19
Memory and PCMCIA Control Module
The RT fields in the MSCx registers specify the type of memory (burst-of-four ROM, burst-of-eight
ROM, nonburst ROM, Flash, SRAM) and the RBW fields specify the bus width for the memory space
selected by nCS<3:0>. If a 16-bit bus width is specified, transactions take place across data pins
D<15:0>.
10.4.1 ROM Interface Overview
The SA-1100 provides programmable timing for both burst and nonburst ROMs. The RDF field in
MSCx is the latency (in memory clock cycles) for nonburst ROMs and the first data beat of a burst
ROM. RDN is the latency for the burst data beats after the first for burst ROMs. RRR delays the
following access to a different memory space to allow time for the current ROM to tristate the data
bus. This parameter should be programmed with the maximum tOFF value, as specified by the
ROM manufacturer. One memory clock cycle is added to each of these parameters. At power-on
reset, the SMCNFG0 field in the MSC0 register is initialized such that the RDF, RDN, and RRR
fields are set to their maximum values to accommodate the slowest ROMs at initial boot; RT is set
to be nonburst ROM; and RBW0 is loaded with the value of the inverse of the ROM_SEL pin. The
remaining fields in MSC0 and MSC1 are not initialized on power-on reset. MSC0:SMCNFG0 is
selected when the address space corresponding to nCS0 is accessed.
The SA-1100 supports a ROM burst size of 1, 4, or 8 words. A single DRAM CBR refresh cycle
may be inserted between word accesses within a transaction. nCS and nOE are deasserted during
the refresh cycle.
10.4.2 ROM Timing Diagrams and Parameters
Figure 10-6, Figure 10-7, and Figure 10-8 show the timing for burst and nonburst ROMS.