Cypress manual CY8CTST120, CY8CTMG120, CY8CTMA120

CY8CTST120, CY8CTMG120, CY8CTMA120

3.Invalid Flash reads may occur if Vdd is pulled to -0.5V just before power on.

PROBLEM DEFINITION

When Vdd of the device is pulled below ground just before power on, the first read from each 8K Flash page may be corrupted. This issue does not affect Flash page 0 because it is the selected page upon reset.

PARAMETERS AFFECTED

When Vdd is pulled below ground before power on, an internal Flash reference may deviate from its nominal voltage. The reference deviation tends to result in the first Flash read from that page returning 0xFF. During the first read from each page, the reference is reset. This results in all future reads returning the correct value. A short delay of 5 µs before the first real read provides time for the reference voltage to stabilize.

WORKAROUND

To prevent an invalid Flash read, a dummy read from each Flash page must occur before use of the pages. A delay of 5 µs must occur after the dummy read and before a real read. The dummy reads occurs as soon as possible and must be located in Flash page 0 before a read from any other Flash page. An example to read a byte of memory from each Flash page follows. Place it in boot.tpl and boot.asm immediately after the ‘start:’ label.

//dummy read from each 8K Flash page

//page 1

mov A, 0x20	// MSB
mov X, 0x00	// LSB
romx

// wait at least 5 µs mov X, 14

loop1: dec X jnz loop1

4.PMA Index Register fails to auto increment with CPU_Clock set to SysClk/1 (24 MHz).

PROBLEM DEFINITION

When the device is operating at 4.75 to 5.25V and the CPU_Clock is set to SysClk/1 (24 MHz), the USB PMA Index Register may fail to increment automatically when used in an OUT endpoint configuration at full speed. When the application program attempts to use the bReadOutEP() function, the first byte in the PMA buffer is always returned.

PARAMETERS AFFECTED

An internal flip-flop hold problem associated with Index Register increment function. All reads of the associated RAM originate from the first byte. The hold problem has no impact on other circuits or functions within the device.

WORKAROUND

To make certain that the index register properly increments, set the CPU_Clock to SysClk/2 (12 MHz) during the read of the PMA buffer. An example for the clock adjustment method is listed below.

PSoC Designer™ 4.3 User Module Workaround: PSoC Designer Release 4.3 and subsequent releases includes a revised full speed USB User Module, which includes the revised firmware as shown in the following example.

;;

;; 24Mhz read PMA workaround

;;

M8C_SetBank1

mov A, reg[OSC_CR0] push A

September 25, 2008 Document No. 001-49038 Rev. ** 3

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