User`s manual

46 RabbitCore RCM2000
A.2 Bus Loading
You must pay careful attention to bus loading when designing an interface to the RCM2000. This
section provides bus loading for external devices.
Table A-2 lists the capacitance for the various RCM2000 I/O ports.
Table A-3 lists the external capacitive bus loading for the various Rabbit 2000 output
ports. Be sure to add the loads for the devices you are using in your custom system and
verify that they do not exceed the values in Table A-3.
Table A-2. Capacitance of RCM2000 I/O Ports
I/O Ports
Input Capacitance
(pF)
Output Capacitance
(pF)
Typ. Max. Typ. Max.
Parallel Ports A to E 6 pF 12 pF 10 pF 14 pF
Data Lines D0–D7 16 pF 30 pF 24 pF 32 pF
Address Lines A0–A12 — — 24 pF 32 pF
Table A-3. External Capacitive Bus Loading -40°C to +85°C
Output Port
Clock Speed
(MHz)
Maximum External
Capacitive Loading (pF)
A[12:1]
D[7:1]
25.8 50
A[12:1]
D[7:1]
18.4
55 for 90 ns flash
100 for 55 ns flash
*
* The RCM2020 operating at 18.4 MHz will typically come with a
flash EPROM whose access time is 55 ns. Because of the volatil-
ity of the memory market, a 90 ns flash EPROM could be used on
the RCM2020.
A0
D0
25.8, 18.4 100
PD[3:0] 25.8, 18.4, 100
PA[7:0]
PB[7,6]
PC[6,4,2,0]
PD[7:4]
PE[7:0]
25.8, 18.4 90
All data, address, and I/O
lines with clock doubler
disabled
12.9, 9.2 100