Maxim Integrated MAXQ7666 - Manual (Page 317)

SECTION 12: IN-SYSTEM PROGRAMMING
The MAXQ7665/MAXQ7666 are equipped with a bootstrap loader as part of the utility ROM firmware. The main function of the boot-
strap loader is to provide in-system programming capability to the user application. The MAXQ7665/MAXQ7666 in-system program-
ming features include:
• Standard JTAG/TAP interface based communication
• Built-in JTAG bootstrap loader for flash programming and verifying
• Password lock protection to access bootstrap loader operations
12.1 Bootstrap-Loader Mode
Internal flash memory for the MAXQ7665/MAXQ7666 can be initialized through bootstrap-loader mode. To enable the bootstrap loader
and establish a desired communication channel, the system programming instruction (100b) must be loaded into the TAP instruction
register using the IR-scan sequence. Once the instruction is latched in the instruction parallel buffer (IR2:IR0) and is recognized by the
TAP controller in the update-IR state, a 3-bit data shift register is activated as the communication channel for DR-scan sequences. The
TAP retains the system programming instruction until a new instruction is shifted in or the TAP controller returns to the test-logic-reset
state. This 3-bit shift register formed between the TDI and TDO pins is directly interfaced to the 3-bit serial programming buffer (SPB).
The SPB contains three bits with the following functions:
• SPB.0: System Programming Enable (SPE). Setting this bit to logic 1 denotes that system programming is desired upon exit-
ing reset. When it is cleared to logic 0, no system programming is needed. The reset vector examines the logic state of SPE in
the utility ROM to determine the program flow after a reset. When SPE = 1, the bootstrap loader selected by the PSS1:PSS0 bits
are activated to perform a bootstrap-loader function. When SPE = 0, the utility ROM transfers execution control to the normal user
program.
• SPB.2 and SPB.1: Programming Source Select (PSS1:PSS0). These bits allow the host to select programming interface
sources. The PSS bits have no functions when the SPE bit is cleared.
Note: The MAXQ7665/MAXQ7666 utility ROM bootstrap loader supports only JTAG as the programming source (see Table 12-1).
The DR-scan sequence is used to configure the SPB bits. The data content of the SPB register is reflected in the ICDF register and
allows read/write access by the CPU. These bits are cleared by power-on reset or test-logic-reset of the TAP controller.
MAXQ7665/MAXQ7666 User’s Guide
12-2
Table 12-1. Programming Source Select Decode
PSS1 PSS0 PROGRAMMING SOURCE
0 0 JTAG
0 1 Reserved
1 0 Reserved
1 1 Reserved
Maxim Integrated