C8051F52x-53x
22.2. C2 Pin Sharing
The C2 protocol allows the C2 pins to be shared with user functions so that in-system debugging and
Flash programming functions may be performed. This is possible because C2 communication is typically
performed when the device is in the halt state, where all on-chip peripherals and user software are stalled.
In this halted state, the C2 interface can safely ‘borrow’ the C2CK (/RST) and C2D (P2.7) pins. In most
applications, external resistors are required to isolate C2 interface traffic from the user application. A typi-
cal isolation configuration is shown in Figure 22.1.
C8051Fxxx
/Reset (a)
Input (b)
C2CK
C2D
Output (c)
C2 Interface Master
Figure 22.1. Typical C2 Pin Sharing
The configuration in Figure 22.1 assumes the following:
1. The user input (b) cannot change state while the target device is halted.
2. The /RST pin on the target device is used as an input only.
Additional resistors may be necessary depending on the specific application.
Rev. 0.3
219
SILICON [ SILICON ]
