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BCK5-BCK0 The refresh rate is defined by the following equation:
PROM Access Time Control Register
The MVME172 is populated with a 150ns PROM memory device. Due to
the wide range of PROM speeds, the contents can be changed by software
to adjust for a specific speed.
ADR/SIZ
BIT
23
NAME
OPER
R
RESET
0
ET2-ET0 PROM access time is controlled by the state of ET2-ET0.
http://www.mcg.mot.com/literature
Refresh Rate = BCK/BUS CLOCK * 16
where BCK is the value programmed in the Bus Clock
Register, and BUS CLOCK is the MC68xx060 bus clock
frequency.
$FFF42040 (8 bits)
22
21
20
ROM0
R
R
R/W
0
0
1 PL
The following table defines the ET2-ET0 encoding (note
that for the MVE172, whose bus frequency is
processor frequency, only the 33MHz column applies).
ET2-
PROM Access <= N
ET0
at 25 MHz where N =
$0
$1
$2
$3
$4
$5
$6
$7
Programming Model
19
18
ET2
R
R/W
0
1 PL
PROM Access <= N
at 33 MHz where N =
60 ns
100 ns
140 ns
180 ns
220 ns
260 ns
300 ns
340 ns
17
16
ET1
ET0
R/W
R/W
1 PL
1 PL
1
/
the
2
40 ns
70 ns
100 ns
130 ns
160 ns
190 ns
210 ns
240 ns
3-39
3
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