RAM Area
The on-board dynamic RAM area is used for the exception vector table of the CPU, as a
scratch pad RAM for the Resident Monitor and for user program/data. The RAM area
has a capacity of 128k bytes on PME68-1B/100 and /101 and 512k bytes on /102 and /103.
Typical access time is 280ns if no refresh cycle is taking place.
RAM Refresh
Refresh of the dynamic RAM is accomplished by performing a memory cycle lasting 15
microseconds to each of the 128 row addresses, at intervals of 2ms. The use of a "RAS
Only Refresh" signal results in a substantial reduction in operating power. For real time
operations the refresh is fully asynchronous to the LOCAL and VMEbuses. The refresh
process is completely transparent to the user.
When a refresh request is pending, a delay of 300ns (maximum) is required before
attempting to access the memory. This delay is due to refresh having a higher priority.
RAM Timing
The DRAMs are high performance devices ideal for real-time applications. Device
access time is typically 150ns with a board access time of 285ns minimum. This time is
extended if a refresh cycle is pending.
RAM Summary
Start address
$000008
End address a)
$01FFFF (128k bytes)
End address b)
$07FFFF (512k bytes)
Boundary a)
$020000 (128k bytes)
Boundary b)
$080000 (512k bytes)
Access modes
Byte or Word
Read or Write
Usable data bits
D0 to D7 and D8 to D15
Access time
285ns (min)
320ns (typ)
600ns (max) with Refresh
PME68-1B Manual
Page 15 Issue 5
Содержание PME 68-1B
Страница 8: ...Figure 1 The PME 68 1B Board Photograph not available in PDF PME 68 1B Manual Page 2 Issue 5...
Страница 12: ...Figure 4 Component Layout Diagram P5 P4 P3 BAT PME 68 1B Manual Page 6 Issue 5...
Страница 56: ...Figure 14 Link Areas BAT PME68 1B Manual Page 50 Issue 5...
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Страница 59: ...Figure 15 Location of System EPROM Area 1 2 3 4 1 2 3 4 WC1 WC2 PME68 1B Manual Page 53 Issue 5...
Страница 80: ...Figure 41 Location of BERR Jumpers 1 2 3 4 WK1 WK2 BR26 2 3 1 BAT PME68 1B Manual Page 74 Issue 5...
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