C8051F300 Datasheet, PDF (173/176 Pages) List of Unclassifed Manufacturers – Mixed Signal ISP Flash MCU Family

C8051F300/1/2/3/4/5
17.2. 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 (normally RST) and C2D (normally P0.7)
pins. In most applications, external resistors are required to isolate C2 interface traffic from the user appli-
cation. A typical isolation configuration is shown in Figure 17.1.
C8051F300
/Reset (a)
Input (b)
Output (c)
C2CK (/RST)
C2D (P0.7)
C2 Interface Master
Figure 17.1. Typical C2 Pin Sharing
The configuration in Figure 17.1 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.
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