Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 19 of 30

Testwrite

Testwrite means that the word to be programmed is simply written to an on-chip shift register so that the resulting behavior of

the AS8118 device may be examined. Once the PROM word is confirmed correct, it may be burned into the device. i.e.

Irreversibly written to the AS8118.

Until the data has been burned into the device, in other words, if only a Testwrite procedure has been performed, the data

will be lost when the supply is removed from the AS8118 device.

Due to the respective on-chip processing it is required to testwrite the inverse of the word to be programmed. Continuing with

the above example the word defined in the example should be as follows:

69

68

67

66

65

64

63

62

61

60

59

58

57

56

55

54

53

52

51

1

1

1

1

111

1111

1111

1111

50

…

34

333231

30292827

26252423

22212019

1

…

1

110

1101

0101

1100

18

17

16

15

14

13

12

11

10

98

7654

3210

1

0

1

0

110

0100

1010

1110

The Testwrite procedure is carried out as described in the following timing diagram:

TM

DIRO

PROG

69

68

67

4

3

0

1

2

Startup

define

testwrite

mode

xH

x

L

H

f1

t2

t3

Imax:

500

µA

start

testwrite

(DIRO=0)

High

Low

High

Low

3V-3.5V

0V

H

H

L

Note: High and Low refers to VDD and VSS respectively.

On the first falling TM edge the mode (Testwrite) is defined. On the next rising TM edge the procedure is started. Afterwards

70 clocks have to be sent to DIRO. As can be seen the logic level on PROG prior to the positive DIRO edges defines the

state to be shifted into the internal register.

Important timing parameters are:

f1: Maximum frequency, must not exceed 50kHz

t2: Data setup time, minimum is 100ns

t3: Data storage time: the programmed bit is stored after approximately 20ns

Burn

The Burn procedure irreversibly writes data to the PROM. To do this, the 1s in the original word to be programmed must be

burned.