============================================================================= AST RESEARCH, INC. TECHNICAL BULLETIN #0610 02-07-90 ============================================================================= SERIAL PORT PARITY ERRORS Under certain circumstances, the serial ports on some Premium computers may exhibit parity errors during serial data transmission. The problem manifests itself as a bad parity bit when transmitting data with 8 Bits, 1 Stop Bit and Even Parity. The problem is caused by an anomaly in the Zymos 16C451 and 16C452 Dual UART serial controller chips that were once used on some Premium motherboards. Users experiencing this problem can resolve the problem in either of the following ways: 1. Change the data transmission parameters from; 8 Bits, 1 Stop Bit, Even Parity, to; 8 Bits, 1 Stop Bit No Parity. 2. Contact your AST Authorized Service Center and arrange for the replacement of the system's motherboard. ASSEMBLIES AFFECTED: Chip Identification: Chips can be identified by observing the soldered-in chips at the following locations. These chips will be labeled either, "ZYMOS 16C451" or "ZYMOS 16C452". AST DESCRIPTION PART NUMBER CHIP LOCATION PCB Premium Motherboard 202273-00X U104 PCB Premium Motherboard 202356-00X U104 PCB WS 386SX Motherboard 202276-00X U123 PCB Bravo 386SX Motherboard 202343-00X U9 PCB Bravo 286 Motherboard 202286-00X U6