User`s manual

42 RabbitCore RCM2300
A.2 Bus Loading
You must pay careful attention to bus loading when designing an interface to the
RCM2300. This section provides bus loading information for external devices.
Table A-2 lists the capacitance for the various Rabbit 2000 I/O ports with SRAM and flash
memory connected.
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 system and verify that
they do not exceed the values in Table A-3.
The values from the table above are derived using 55 ns (flash memory) and 70 ns
(SRAM) memory access times. External capacitive loading can be improved by 10 pF for
commercial temperature ranges, but do not exceed 100 pF. See the AC timing specifica-
tions in the Rabbit 2000 Microprocessor Users Manual for more information.
Table A-2. Capacitance of Rabbit 2000 I/O Ports with External Memory
I/O Ports
Input
Capacitance
(pF)
Output
Capacitance
(pF)
Parallel Ports A to E 12 14
Data Lines D0–D7 30 32
Address Lines A0–A12 — 32
Table A-3. External Capacitive Bus Loading -40°C to +85°C
Output Port
Clock Speed
(MHz)
Maximum External
Capacitive Loading (pF)
A[4:1]
D[7:1]
22.1 50
A[4:1]
D[7:1]
22.1 100 for 55 ns flash
A0
D0
22.1 100
PD[3:0] 22.1 100
PA[7:0]
PB[7,6]
PC[6,2,0]
PD[7:0]
PE[7:0]
22.1 90
All data, address, and
I/O lines with clock
doubler disabled
11.06 100