AN987 Datasheet, PDF (4/10 Pages) STMicroelectronics – ST7 SERIAL TEST CONTROLLER PROGRAMMING

ST7 SERIAL TEST CONTROLLER PROGRAMMING
If these pins need to be tied to V_DD or V_SS, or if they are used by the user’s application, they
must be isolated from the user circuitry during programming. To do so, a jumper can be
added for each of the eight pins (see Figure 2.).
Note: Isolation resistors (47 kΩ) can be used instead of jumpers only if these pins are used
by the application as input (without Pull-up, without pull-down, or analog input configura-
tion).
s 3 system pins, VPP/TEST, RESET and OSCIN, which must be connected as follows:
– The VPP/TEST pin must not be directly connected to GND/V_SS on the application board
in order to avoid any conflict with the programming voltage. This pin should be pulled down
by a 10 kΩ resistor (see Figure 2.).
– The RESET pin controls the entry into programming mode. This pin must be connected to
a 10 kΩ pull-up resistor and a 1 nF capacitor connected to GND (see Figure 2.) to avoid
any direct connections to V_SS. This pin can be connected to a 47 kΩ isolation resistor if an
external reset is provided by the application board.
– The OSCIN pin synchronizes the programming operation using a clock generated by the
programming tool. The OSCIN pin can be directly connected to the J1 connector. No iso-
lation is needed as long as a quartz crystal or ceramic resonator is used in the application.
If an external clock generator is used in the application, it must be disconnected during
STC programming.
Note: The OSCOUT pin does not need to be disconnected during the programming phase
as long as a crystal, a ceramic resonator or an external clock source is used to drive the
internal oscillator (user mode only).
s The V_DD and V_SS power supply pins. The use of the V_DD connection is optional, depending
on whether the application board supply can be disconnected or not.
If the application board supply is disconnected, the chip can be supplied through the
programming tool (as long as the total current load does not exceed 100 mA and the
capacitive load is less than 50 µF). In this case, only 1 jumper needs to be added in order to
disconnect the V_PP pin from the user circuitry during the programming sequence. No jumper
is needed for V_SS (see Figure 2.).
If you want to use the application board power supply, its voltage must be 5 V, so that logic
levels are compatible with those of the programming tool.
Note: In any case, the ground from the application board and the ground from the
programming tool must be connected together (see Figure 2.).
4/10