Vault 7: Projects
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PIC24F Family Reference Manual
DS39716A-page 33-8 Advance Information © 2006 Microchip Technology Inc.
33.4.3 Boundary Scan Register (BSR)
The BSR is a large shift register that is comprised of all the I/O Boundary Scan Cells (BSCs),
daisy-chained together (Figure 33-5). Each I/O pin has one BSC, each containing 3 BSC regis-
ters: an input cell, an output cell and a control cell. When the SAMPLE/PRELOAD or EXTEST
instructions are active, the BSR is placed between the TDI and TDO pins, with the TDI pin as the
input and the TDO pin as the output.
The size of the BSR depends on the number of I/O pins on the device. For example, the
PIC24FJ128GA010 has 82 I/O pins. With 3 BSC registers for each of the 82 I/Os, this yields a
Boundary Scan register length of 246 bits. Information on the I/O port pin count of other PIC24F
devices can be found in their specific device data sheets.
Figure 33-5: Daisy-Chained Boundary Scan Cell Registers on a PIC24F Microcontroller
33.4.3.1 BOUNDARY SCAN CELL (BSC)
The function of the BSC is to capture and override I/O input or output data values when JTAG is
active. The BSC consists of three Single-Bit Capture register cells and two Single-Bit Holding
register cells. The capture cells are daisy-chained to capture the port’s input, output and control
(output-enable) data, as well as pass JTAG data along the Boundary Scan register. Command
signals from the TAP controller determine if the port of JTAG data is captured, and how and when
it is clocked out of the BSC.
The first register either captures internal data destined to the output driver, or provides serially
scanned in data for the output driver. The second register captures internal output-enable control
from the output driver and also provides serially scanned in output-enable values. The third
register captures the input data from the I/O’s input buffer.
I C O
I C O
I C O
O
C
I
O
C
I
O
C
I
I
C
O
I
C
O
I
C
O
TAP Controller
PIC24F
Internal
Logic
I/O Pin
TDI TMS TCK TDO
BSC with Three Register Cells:
• Input Cell (I)
• Control Cell (C)
• Output Cell (O)
Protego_Release_01_05-Related-OEM-Documentation-PIC24FJ32MC10X-Reference_Manual-Section33-Programming_and_Diagnostics.pdf