Converting STK25C48 to STK12C68 Introduction r u ST si K1 ng 2 C C6 Y1 8 4E is 25 in N 6L R A ND in st St ea at d us of . ST K1 2C 68 . This document provides guidance on converting a design that is currently using the STK25C48 to the Simtek recommended part STK12C68 Feature set and limitations of theSTK25C48 Function Category STK25C48 Autostore Yes, by specified slow VCC fall rate Software store Software recall Yes Yes Package Comparison STK12C68 Wire for immunity from ramp rate by using a 68uf capacitor Yes Yes The STK25C48 is only available in the 24 pin 600mil plastic dip package. The closest package is the 600 mil 28 pin PDIP and being larger may cause layout difficulty. Package PKG Code S STK25C48 Not available STK12C68 Available 600 mil pdip -- 28 pin 300 mil cdip -- 28 pin 600 mil pdip -- 24pin W C W Available Not available Not available Available Available Available C on si de 350 mil SOIC – 28 pin Notes Surface mount – smallest PCB area Through hole Through hole Through hole Issues to consider during the conversion The key difference is that the STK25C48 has been internally configured to autostore but does not use a 68uf capacitor. This means there is no protection from power that falls too fast. This is no longer a recommended application and is no longer supported by Simtek. The STK12C68 will be wired using the 68uf power storage capacitor on the VCAP pin. The converted STK12C68 application will then be fully immune from the minimum ramp rate requirement. This application will process an autostore using power stored on a 68uf capacitor. Also, the new HSB signal is unused. All other pins have the same function. Application Note Number MA0022 0.0 Schematic changes for conversion: This is a feature upgrade and conversion of the STK25C48 to the mainstream STK12C68. Applications requiring a minimum ramp rate are no longer supported or recommended. So, this conversion is to the full featured STK12C68 application with autostore being powered from a storage capacitor. This requires the addition of a 68uf capacitor and wired to VCAP pin 1. Also, the bypass capacitor moves to the VCAP pin. The choice of package is open with the “S” package being the most area efficient surface mount choice. 8 7 6 5 4 3 2 1 23 22 19 /READ 20 /CE 18 /WRITE 21 A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 G E W VSS from power plane +5v 9 10 11 13 14 15 16 17 DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 C1-bypass 0.1 uF . A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 24 68 VCC 12 must use gnd plane STK25C48 Before Conversion schematic r u ST si K1 ng 2 C C6 Y1 8 4E is 25 in N 6L R A ND in st St ea at d us of . ST K1 2C U1 In this conversion, old bypass capacitor C1 is moved from +5v on pin 24 to pin 1. The storage capacitor C2 is added to pin 1 and system power is connected to pin 28. The 12C69 pins 23 and 2 (A11 and A12) are tied low or you may utilize the additional memory space. ( If you expand the space, be sure to expand the memory space in the /E logic decoding). The new signal /HSB is left open and unused. 10 9 8 7 6 5 4 3 25 24 21 23 2 not used /READ /CE /WRITE 26 22 20 27 VCAP A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 VCCx DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 +5v 28 11 12 13 15 16 17 18 19 de A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 U1 si 1 DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 C closest to pin Moved from VCC C1-bypass 0.1uF on C2-storage 68 uF, 6.3v min. HSB G E W VSS 14 STK12C68 After Conversion schematic must use gnd plane On the next page, pin by pin comparisons of the two show all pins are the same except for the bypass capacitor moving to pin 1 and connected to system power, +5v. Application Note Number MA0022 0.0 Corresponding pin Connections Pin for pin comparison of the two parts is given in the table below: de 21 24 si 22 23 on Pin Comments Must connect 0.1UF BYPASS and 68uf, 6.3v min. Tie to gnd No change “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ Tie to gnd No change “ LEAVE OPEN UNUSED No change This pin now must continue to be connected to +5v, bypass of 0.1uF is ok but unneeded. . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 68 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 STK12C68 NAME VCAP A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS DQ3 DQ4 DQ5 DQ6 DQ7 E# A10 G# A11 A9 A8 HSB W# VCCX r u ST si K1 ng 2 C C6 Y1 8 4E is 25 in N 6L R A ND in st St ea at d us of . ST K1 2C Pin C STK25C48 NAME --none---none-A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS DQ3 DQ4 DQ5 DQ6 DQ7 E# A10 G# --none-A9 A8 --none-W# VCC Application Note Number MA0022 0.0