Instruction Manual

4-9 ___________________________________________________________________________________________________________

MAXQ7667 User’s Guide

4.1.6 System Control Register (SC)

Bit 7: Test Access (JTAG) Port Enable (TAP).

This bit controls whether the Test Access Port special-function pins are enabled. The

TAP defaults to being enabled. Clearing this bit to 0 disables the TAP special function pins. See

Section 11 for more information about

JTAG and TAP.

Bits 6 and 0: Reserved. Read 0, write ignored.

Bits 5 and 4: Code Data Access Bits 1 and 0 (CDA[1:0]). The CDA bits are used to logically map physical program memory page

to the data space for read/write access (see table below).

The logical data memory addresses of the program pages depend on whether execution is from Utility ROM or logical data memory.

Note that CDA1 is not implemented if the upper 32k of the program space is not used for the user code. No CDA bits are needed if

only one page of program space is incorporated. (P0 is the only memory available in the MAXQ7667.)

Bit 3: Upper Program Access (UPA). The physical program memory is logically divided into four pages; P0 and P1 occupy the lower

32KWords while P2 and P3 occupy the upper 32KWords. P0 and P1 are assigned to the lower half of the program space and are always

active. P2 and P3 must be explicitly activated in the upper half of the program space by setting the UPA bit to 1. When UPA bit is

cleared to 0, the upper program memory space is occupied by the utility ROM and the logical data memory, which is accessible as

program memory. Note that the UPA is not implemented if the upper 32K of the program space is not used for the user code.

Bit 2: ROM Operation Done (ROD). This bit is used to signify completion of a ROM operation sequence to the control units. This allows

the debug engine to determine the status of a ROM sequence. Setting this bit to logic 1 causes an internal system reset if the JTAG

SPE bit is also set. Setting the ROD bit will clear the JTAG SPE bit if it is set and the ROD bit will be automatically cleared by hardware

once the control unit acknowledges the done indication. See

Section 12 for more information.

Bit 1: Password Lock (PWL). This bit defaults to 1 on a power-on reset. When this bit is 1, it requires a 32-byte password to be

matched with the password in the program space before allowing access to the password protected in-circuit debug or bootstrap

loader ROM routines. Clearing this bit to 0 disables the password protection for these ROM routines. See

Section 13 for more

information.

Bit #

76543210

Name TAP — CDA1 CDA0 UPA ROD PWL —

Reset 1 0 0 0 0 0 1 0

Access rw r rw rw rw rw rw r

r = read, w = write

Note: Bit 1 (PWL) is set to 1 on a power-on reset only.

C D A [1 :0]

BYTE MODE

A C TIVE PAGE

WO R D MO DE

A C TIVE PAGE

00 P0 P0 and P1

01 P1 P0 and P1

10 P2 P2 and P3

11 P3 P2 and P3