TUSB5052 datasheet(20/84 Pages) TI

20 / 84 page

4–2

4.1

Miscellaneous Registers

4.1.1

ROMs: ROM Shadow Configuration Register

This register is used by the MCU to switch from boot mode to normal operation mode (boot mode is set on

power-on-reset only). In addition, this register provides the device revision number and the ROM/RAM configuration.

ROA

SDW

R/O

R/W

BIT

NAME

RESET

FUNCTION

SDW

This bit enables/disables boot ROM. (Shadow the ROM)

SDW = 0

When clear, the MCU executes from the 6K boot–ROM space. The boot ROM appears in

two locations: 0000 and 8000h. The 16K RAM is mapped to XDATA space; therefore,

read/write operation is possible. This bit is set by the MCU after the RAM load is com-

pleted. MCU cannot clear this bit; it is cleared on power-up-reset or function-reset.

SDW = 1

When set by the MCU, the 6K boot-ROM maps to location 8000h, and the 16K RAM is

mapped to code space, starting at location 0000h. At this point, the MCU executes from

RAM, and the write operation is disabled (no write operation is possible in code space).

4–1

R[3:0]

No effect

These bits reflect the device revision number

6–5

S[1:0]

No effect

Code space size. These bits define the ROM or RAM code-space size (ROA bit defines ROM or

RAM). These bits are permanently set and are not affected by reset (see Table 4–1)

00 = 4K bytes code space size

01 = 8K bytes code space size

10 = 16K bytes code space size

11 = 32K bytes code space size

ROA

No affect

ROM or RAM version. This bit indicates whether the code space is RAM or ROM based. This bit is

permanently set and is not affected by reset (see Table 4–1)

ROA = 0 Code space is ROM

ROA = 1 Code space is RAM

Table 4–1. ROM/RAM Size Defintion Table

ROMS REGISTER

Boot ROM

RAM CODE

ROM CODE

ROA

Boot-ROM

RAM CODE

ROM CODE

None

16K (reserved)

None

32K (reserved)

None

16K

None

32K (reserved)

None

4.1.2

Boot Operation (MCU Firmware Loading)

Since the code space is in RAM (with the exception of the boot ROM), the TUSB5152 firmware must be loaded from

an external source. Two sources are available for booting: one from an external serial E2PROM connected to the I2C

bus, and the other from the host via the USB. On device reset, the SDW bit (in ROMS register) and CONT bit (in

USBCTL: USB control register) are cleared. This configures the memory space to

boot-mode (see Memory-Map) and

keeps the device

disconnected from the host. The first instruction is fetched from location 0000h (which is in the

6K-ROM). The 16K-RAM is mapped to XDATA space (location 0000h). The MCU executes a read from an external

E2PROM and tests whether it contains the code (by testing for boot-signature). If it contains the code, the MCU reads

from E2PROM and writes to the 16K-RAM in XDATA space. If it does not contain the code, the MCU proceeds to boot

from the USB.

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